I'm doing this rather backwards, as I started with a newer posturpedic that felt like I was sleeping on concrete, but also have a large depression where I had been sleeping.

I'm very happy with the 3" soft latex from FBM, (does not run hot) but there is still the depression, and I would still like it a bit softer.  The depression remains when I rotate mattress or topper, so it has to be box spring.  So do I replace it with slats or something solid?  I understand the idea of slats letting the mattress breathe, but others say you end up with a roller coaster surface which would drive me nuts.  Also I would have to modify my bed to use slats.  Would it be crazy to just put slats or a slab of plywood on top of the existing boxspring?

I'm just coming back from cancer so am fighting insomnia as it is (chemo side affect apparently) so not fighting my bed would be great.

Thanks!

Sleep deprived.

Most often the depression is in the foam in your mattress.  The major companies use cheap polyurethene foam now, that forms indentations.   This problem is the worst in pillowtops, but it sounds like you don't have one of those.   When you rotate, are you sleeping in the same spot on the mattress (probably the middle)?

What kind of box spring do you have?  Is it new?  If you press on it do you find any weak spots or indentations?  The new ones are usually very firm, with little give to them.

I have a fairly new Sealy Posturpedic that I cut open open, removed all of the foam, and replaced with higher quality latex and memory foam.  It is much better than the way the mattress was orgininally made.