I have researched and made my own mattresses for 3 beds because no commercial product seemed hard enough.
I now need to select the right foam for my tent trailer to replace the ridiculous mattresses they include. The problem is I can only fit a 4" thick mattress. It needs to be very firm and support 250 lbs without bottoming.
I was thinking a 1" 7.1 lb memory foam top with a 3" poly foam bottom.
Would this work?
It would depend to some degree on your sleeping positions and would also depend on what you mean by “work” because it certainly isn’t thick enough for any kind of ideal design but I would use a firmer HR polyfoam in the base (2.5 lbs and higher with a compression modulus of 2.4 or higher) because it has a higher compression modulus which means it can be a little softer on the surface and then become firmer faster as you compress it which can prevent you from bottoming out. It will be more “latex like” than HD polyfoam.
I’m not so sure I would add memory foam in only a 1" layer unless you want “some” of the memory foam feel although with only an inch it won’t have nearly as much memory foam feel to it as a thicker layer and much of what you “feel” will come from the layers below it.
For a 4" “mattress”… I would tend to use a single layer of HR polyfoam in a firmer version and I would test the specific ILD in a local foam shop.
I’m a side sleeper and overweight.