Can a box spring be the root cause of a mattress that is too hard?

I would assume that the box spring could only cause issues related to sag and inconsistent firmess, but maybe I was wrong?

A little back story: My wife and I decided that our 6 year old king mattress (A firm Kingsdown innerspring with some kind of top layer) had either become too hard over time or we’ve aged such that it felt too hard. I’ve had back issues and have been sleeping terribly for the past two years, enough so that I questioned whether I had some kind of hormonal issue going on. I never thought it could be our mattress.

A prolonged time at my father’s house who was sick made me realize that the bed was the culprit. Their guest bed was really soft which I normally hate but my discomfort completely went away and promptly returned once I got home. So we decided to replace our mattress.

We spent a tremendous amount of time researching in person and on this and other sites. We were determined to go as natural as possible so we considered Essentia, Obasan and Ikea latex. In the end, we decided to skip Essentia because of concerns raised on this site and basically go with the cheaper Ikea option and look to buy an Obasan down the road. After three visits to Ikea, the MORGONGÅVA latex felt like a good match.

The Ikea MORGONGÅVA arrives yesterday, they take away our old mattress, we set it up on the existing box springs and are stunned at how hard it feels. It’s nowhere near as soft as it was in the store. In fact, it feels like the old mattress we just got rid of. I was somewhat devastated. I tried the mattress at Ikea on both a boxspring and a slat bed and I definitely preferred the feel of the box spring and figured our box springs would be perfect.

Which makes me wonder if the mattress we just ditched was fine and just needed a new foundation. But isn’t that backwards? Aren’t box springs supposed to provide a certain amount of shock absorption? Could a bad set of box springs make a mattress feel too firm? Could a mattress feel softer on slats or an actual floor than the actual box springs that were bought with the mattress?

I’m somewhat devastated about this. I feel like we might have wasted our money and I’m really not sure how to proceed. Do we buy new boxsprings? (Another $500) Do we try slats? (Our existing slats are too wide for a latex mattress.) Am I misdiagnosing the whole situation? Is the firmness via the box springs caused by the fact that they are split king box springs?

btw - The best I have for the name of the old mattress is from the mattress tag: ‘78" Grafton NF Firm Matt - Brenda’ which brings nothing up on google. But it was definitely a Kingsdown. We spent $1500 on the mattress/box springs.

Hi OsbourneCox,

An “active” support system under a mattress can have a considerable effect on how it feels and performs and it will vary depending on the specifics of the support system. When you are testing mattresses with flexible support systems underneath them then it’s usually best to treat the support system as part of the sleeping system and purchase the specific set that was the best match for you in terms of PPP because if your box spring is firmer than the box spring or slat system you tested the mattress on in the store then it could certainly account for the difference in how it feels.

There will also be a break in and adjustment period for any new mattress as well and there are some additional suggestions in post #2 here that may also be helpful.

There is more information about the types of support systems that are generally best for different types of mattresses in the foundation post here (and the two posts it links to in the second paragraph) but a box spring or any “active” part of a sleeping system can certainly affect the feel and performance of a sleeping system. In most cases using a non flexing foundation will make the mattress feel firmer but sometimes the effect of different components can be surprising. There are different types of firmness and softness that some people can be more or less sensitive to (see post #15 here) and by firming up the support system under a mattress it can also “force” more of the compression to the top layer of the mattress which for some people may “feel” what they “translate” as being softer so the individual effects of different components can be different for different people and the only “rule” is that personal experience always “trumps” theory.

If your mattress is too firm then you still have good options to make if softer with a topper and it’s certainly less risky to buy a mattress that is too firm than one that is too soft. The only way to really know the cause of your experience though would be through a process of elimination based on trial and error. For example you could test the effect of your box spring vs a rigid foundation by putting your mattress on the floor to see the specific difference that it makes.


We just got a new polyfoam (no springs) mattress a little less than two weeks ago. The first week, we had the mattress on a “adjustable” flexible slat foundation. After one week, we switched to a wood knock down slat foundation- the mattress is firmer for sure.

But I’ve also noticed in the two weeks we’ve had the mattress, that the foam might be getting a tiny bit softer. As I’ve read here at MU, and learned from talking to the manufacturer of our mattress (Tuft and Needle), any mattress can take a few weeks to a couple of months to break in- both the mattress is “breaking in” and our body adjusting to a new mattress- and this seems to true with our new mattress. If it hadn’t been for Phoenix’s suggestions, and the excellent customer service at Tuft and Needle, I probably would have gotten rid of the mattress already!

I’ve laid at and tested the mattresses and foundations at ikea, and wouldn’t be surprised if your boxspring is firmer than what they sell, especially the flexible slat foundation, but even the box spring that I pressed down on in the store, didn’t seem very firm to me… Their foundations are pretty affordable, you don’t have to spend $500 for a new foundation…

By the way, I’m not sure what type of top layers your new mattress has, but I was surprised to find that our new mattress feels better with thinner layers on top, not the thick, overstuffed polyfill mattress pad that was on our old mattress. I thought a thick soft layer would soften up our firm mattress, and it just made things worse…