The original mattress was a one piece foam cushion about 4" thick. Each morning I'd wake up with a back ache - if I didn't wake up in the middle of the night from various pains.
We contracted with a local sailormaker (John Bartlett of Bartlett Sails here in Austin, Texas) to make us a new mattress. He brought out a few samples of various hardness pieces of foam. After trying out several, we chose to build it of two types of foam, one fairly soft, one fairly firm. The soft goes on top, the firm on the bottom. Full thickness - 6".
We now have the most comfortable bed I've slept in. No aches, no pains. Total cost, about $500.