Mattress Forum

The basic mattress model is a comfort layer over a support layer.  Lower back pain and your 'not firm enough' comment (and those through holes in the IKEA mattress profile!) suggests the support layer may not be enough support for your height and weight.

A topper is added to change the comfort layer... to add or replace pressuring relieving comfort.  Adding a topper to increase support layer firmness is made difficult/impractical by the existing intervening comfort layer AND the existing inadequate support layer which will both allow a topper to sag.  Plus the added 'support' won't have any comfort to it... not if it really adds support like a sheet of plywood would add support.  If you are successful, you will end up adding a mattress to your mattress.

You mentioned sleeping on the floor... this becomes more and more unbearable as one grows older.

GK

I am only 5'7 120lb and 27 years of age... not sure if my weight is the issue. I'm not even sure if firmness is my issue because I have slept on softer spring matresses that didn't give me a problem.

I guess why I think firmness is the issue is because I tried sleeping on a 2 inch 4lb 14.5 ILD memory foam on the floor and it was unbearable for my lower back.

I will try my matress on the floor. Although I feel like the foundation gives enough support.. it has plywood that is spaced 3.25 inches apart. If the floor works out should I just put a single piece of plywood over my existing foundation?

I used to sleep on the floor because it was good for my lower back and I didn't sleep on the side too much. Now I am sleeping more on the side.

I just want something simple that won't give me lower back pain.. which is the most sensitive part of my body.

I sleep mostly on my back and sometimes on my side.

Looking to spend only about $500 for a full size.

That platform bed foundation should be ok... should be assembled firm and strong enough.  Your weight should be easily supported by both mattress and foundation.  I see no problems here.  Moving on...

2" of 14ILD is super soft... too soft... not enough to be a comfort layer.  Your body would settle right through it and rest its bearing points on the floor.  Your body would gradually strain and fatigue and become sore.

Given you are not too heavy, the mattress is new, and the foundation looks to be solid... and assuming no related health issue... maybe the problem is that the mattress is too firm... that there is not enough comfort layer depth/softness to cradle your body profile before it settles its bearing points onto the firm support layer?  This would be similar to sleeping on the 14ILD on the floor, although not as severe.  If so, then this can be fixed by adding to the comfort layer... by adding a topper.  You can experiment first by adding a few inches of bedding to increase the comfort layer depth.  If this improves the comfort layer cradling, catching and distributing your weight more evenly to the support layer beneath, then you'll be headed in the right direction and can consider purchasing a topper material like Talalay Latex.

Note that sleeping on your back typically requires less comfort layer cradling/profiling/contouring than sleeping on your side.  Meaning, you may have to add more topper to improve your side sleeping, than you would have to add to improve your back sleeping.  You could add a little (what bedding you can round up) and sleep on your back for a week or two to see if your soreness subsides.  Then take it from there.

GK