I complain about my mattress, out loud, probably four nights out of seven. Not really to my husband, more in his general direction, since he’s usually asleep by the time I start doing it, which is sort of the whole problem I want to get into here. I roll onto my side, I roll onto my back, I do a strange half roll that isn’t really either, and at some point in that rotation I remember, again, that I still haven’t figured out whether the mattress under me is doing its job or whether I’ve just gotten used to it the way you get used to a chair with one short leg.
We live in a triple-decker in Providence that is a hundred and thirty one years old, according to the deed, and every single surface in it has an opinion about temperature, humidity, and apparently now mattress firmness too, because the bedroom floor slopes just enough toward the north wall that I can feel it through a mattress that’s supposedly firm. I found this out properly the winter I bought a “medium firm, universally comfortable” mattress off a very convincing website, put it on the frame, and woke up three nights running feeling like I’d been sleeping slightly downhill, which, as it turns out, I had been, because the house has been quietly settling since roughly the Coolidge administration and nobody warned the mattress about it.
So I’m not going to open this by telling you soft, medium, or firm is the right answer, because I don’t think there is one right answer, I think there’s a right answer for the way you sleep, the shape you’re built, and whoever else happens to be in the bed with you, which is the part almost nobody mentions until it’s 1am and someone’s already asleep on what is very clearly their side of the compromise. I’ve owned four mattresses in eleven years of adult life, which sounds excessive until you count the number of times I’ve genuinely regretted at least three of them, and every single mistake came from skipping the actual thinking part and going straight for whatever the store clerk in Warwick told me was “what most people like.” Most people are not me. Most people also don’t have a bedroom with a two degree slope in it, so we’re already starting from different places.
What I actually want to walk through is how firmness connects to how you sleep, position by position, because that’s the piece that made the whole decision click for me once I finally sat down and thought about it properly, instead of just pressing on mattresses in a showroom for ninety seconds like that tells you anything real about 3am in February.
[Mattress Firmness]
If You Sleep on Your Side
Side sleeping is apparently the most common position in the country, which I only know because I looked it up at 2am one night trying to figure out why my shoulder had gone completely numb again.
If you sleep on your side, your body needs the mattress to do something specific, it needs to let your shoulder and your hip sink in enough that your spine stays roughly straight from neck to tailbone, instead of bridging over a mattress that’s too firm and leaving a gap under your waist that nothing is supporting.
I found this out the hard way with the very firm mattress I bought right after college, the one I chose because it was on sale and because “firm” sounded responsible, like something a grown adult with a real job would sleep on. I woke up for about four months straight with a dead arm, the specific kind of numb where you have to shake it for a full minute before it starts working again, and I genuinely thought that was just a normal part of being a side sleeper until a physical therapist asked what my mattress felt like and looked at me like I’d told her I was sleeping on a park bench.
Soft to medium soft is generally what side sleepers need, something with enough give at the shoulder and hip that you’re not fighting the mattress all night to stay comfortable. Too firm and you get exactly what I got, pressure points and a numb arm. Too soft, and this is the bit people forget, you can sink so far in that your spine curves the wrong way and your lower back starts complaining instead. There’s a real middle zone here, and it’s narrower than the mattress ads make it sound.
[Side Sleepers]
If You Sleep on Your Back
Back sleeping is the position everyone in the mattress industry seems to design for, which makes sense, because it’s the most forgiving position and the easiest to get right with a medium firm mattress. Your weight is distributed fairly evenly, there’s no single joint taking the brunt of it the way a side sleeper’s shoulder does, and what you actually need is support along the length of your spine, particularly your lower back, so it doesn’t sag into a hammock shape over the course of the night.
My husband, Mike, is a back sleeper, flat on his back, hands folded on his chest like he’s auditioning for a Victorian funeral portrait, and he has never once complained about a mattress in the entire time I’ve known him, which used to make me suspicious that he simply doesn’t notice things, until I realized it’s because medium firm mattresses genuinely suit back sleepers without much drama. Lucky him.
Medium to medium firm is the general zone, enough give that your lower back isn’t floating unsupported above the mattress surface, but enough structure that your hips don’t sink lower than your shoulders and pull your spine out of a neutral line. If you’re a back sleeper and you keep waking up with a dull ache low in your back, that’s usually the sag talking, not your posture, and it’s often the first sign a mattress has gone soft in the middle from years of the same two people getting in and out on the same two sides.
[Back Sleepers]
If You Sleep on Your Stomach
Stomach sleeping is the one that gets the least sympathy in every mattress guide I’ve ever read, probably because it’s the least common position and also, frankly, the hardest one to support well. If you sleep on your stomach, you need a firmer surface than either side or back sleepers, because the goal is keeping your hips from sinking lower than the rest of you, which happens fast on a soft mattress and pulls your lower back into a curve it was not built to hold for eight hours.
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A friend of mine spent about a year sleeping on a plush pillow top mattress, stomach down every night, and kept waking up with lower back pain she assumed was from grading papers hunched over a desk, which, fair, teachers hunch, but it turned out to be the mattress letting her hips drop several inches below her shoulders every single night. She switched to a firm mattress, no topper, and the back pain that she’d blamed on desks for a year mostly disappeared within about three weeks.
Firm is really the operative word here, not medium firm, actually firm, because stomach sleepers need the surface to resist sinking more than any other position does. It’s also, worth saying, considered the least ideal position for spinal alignment generally, so if you’re a committed stomach sleeper who’s also getting neck or back pain, firmness helps, but it might not fix everything on its own, and that’s a conversation for a pillow, not a mattress.
[Stomach Sleepers]
Sleeping With a Partner Who Disagrees
Here’s the part nobody mentions in any of this, and it’s the part that actually derailed my last two mattress decisions. All of the above assumes you’re the only person in the bed, deciding based purely on your own sleeping position and your own body weight. The second another person gets in, particularly a person built differently or sleeping differently than you, the whole tidy equation falls apart.
Mike is a heavier, flat on his back sleeper. I’m a lighter side sleeper who moves around more than I’d like to admit.
On a shared mattress, his side needs more firmness to keep from sinking too far and mine needs more give to protect my shoulder and hip, and for a while we were compromising directly into a mattress that suited neither of us particularly well, medium everything, disappointing everyone equally, which I’ve come to think of as the worst kind of compromise, the one where nobody’s actually happy but nobody can point to who ruined it either.
The two real fixes are a mattress with different firmness zones built in, which exist and are worth the extra research even though the marketing around them is exhausting, or accepting that one of you is going to be slightly less catered to than the other and choosing based on whoever’s sleep quality actually suffers more without the right support. We went with a medium firm hybrid with a bit more structure on his side from the coil layer underneath and a softer top layer overall for me, and it took about two weeks of him saying it felt “different, not bad, just different” before he stopped noticing it at all, which I’ve decided counts as a win.
[Sleeping With a Partner]
If You Move All Night and Sleep in Every Position
I am, if I’m honest with myself, this category, and it took me longer than it should have to admit it, because I always thought of myself as a side sleeper until I actually paid attention one night and realized I’d started on my side, ended up on my stomach for a stretch, then flat on my back with one leg hanging off the edge of the mattress like I was trying to escape it. Combination sleepers move through several positions a night, sometimes all of them, and the mattress needs to accommodate all of that rather than being optimized hard for just one.
This is where medium firm earns its reputation as the safe, slightly boring default, because it’s the setting that doesn’t actively fail you in any one position, even if it’s not the absolute best fit for any single one either. It’s the mattress equivalent of ordering the thing on the menu that everyone else at the table will also eat happily, nobody’s favorite, nobody’s enemy.
Responsive materials matter more here than pure firmness rating, actually, because what you want is a mattress that adjusts reasonably fast as you move, rather than one that takes its time catching up to wherever your hip has just relocated to. I learned this after a memory foam mattress that was lovely for the first twenty minutes and then felt like sleeping in a very slow motion trap for the rest of the night every time I changed position, which for me, given how often I change position, was most of the night. A hybrid with some bounce back to it solved that specific problem completely, and I genuinely didn’t know “responsiveness” was something I should have been shopping for until I lived without it.
[Combination Sleepers]
Final Thoughts
If you asked me at the start of all this to just tell you soft, medium, or firm, I couldn’t have, and I still can’t, not without knowing how you actually sleep and who else is in the bed while you’re doing it. What I can tell you is that the answer isn’t really about softness at all, it’s about support in the right places for your particular body in your particular position, and firmness is just the blunt word we’ve all agreed to use for something a lot more specific than that.
My own house has taught me, in its own drafty, hundred and thirty one year old way, that nothing about comfort is one size fits all, not curtains, not radiators, and certainly not a mattress being asked to support two different people with two different bodies on a floor that isn’t even level to begin with. The sloped bedroom didn’t change what I needed from a mattress, but it made me pay attention to it properly for the first time, instead of guessing based on a sale sticker.
So work out your position first, be honest about whether you actually stay in it all night or just start there, then have the slightly awkward conversation with whoever shares the bed about what their body needs too, because that conversation is the one that actually saves you from buying the wrong mattress twice, which I did, and would not recommend.
