I've posted this before, but I'm so pleased with the results, I like boasting about how comfortable my bed is. At the suggestion of another JOF member's post (sorry, I don't remember whom), I put my Target 3" memory foam topper under
my mattress - kind of like a box spring. My Denver mattress is not the pillow-top Jayco now uses, so I also use a 1" thick corrugated foam mattress topper on top
of the bed. I've found this to be the perfect combination of a luxurious, cushy surface, with semi-firm support underneath. And my butt doesn't bottom out on the plywood bed support. The backaches that awakened me every morning from the mattress in my stick-and-bricks, disappeared within a week, once I move into the trailer full time.
I sleep like a baby, and the dog seems to like it, too!