septuagenarian said "In the '70's I slept on foam at BU high rise and within days my back was so bad I was bent over like a 100 year old and couldn't even drive.
I slept on the floor for a few days and all was good again.
To this day I sleep on a mat and have a GREAT back!
Buy a hard, firm mattress and avoid foam or water or air!! "
If you look up any of those brands, you will see that today's foam mattresses are not the same as the foam slabs of the 1970s.