My last mattress i bought off of Amazon as my nephew has them in his house and we stayed there and i really liked it. So he sent me a link and i ordered one. Had it 2 1/2 years now i think and it hasn't sunk or anything and is as good as the day we bought it. It is foam too but isn't hot like some of them i tried. Best thing is it shipped in a box and cost a little over $600 for a king. Here is the link but it is firm! I like it but some might not.
https://www.amazon.com/gp/product/B00EZ5TB4W/?tag=nodakangler10-20
Brokenback, Have you ever tried a waterbed ?
I'm pretty sure that's the one we have, Or something close to it, Price was about the same. Everyone is different but it doesn't work at all for me . Just like clockwork , After 3 hours I wake up with a backache and the only way it goes away is if I walk it off then I'm usually good for another 3 hours . If I happen to sleep longer than 3 hours I have to roll out on the floor and stretch before I can get up. I can sleep on the soft couch and not near as bad, I'm thinking of trying a waterbed again , We had one years ago and I slept like a baby but when we remodeled we got rid of it. Does anyone use a waterbed ?