We threw out the OE mattress a number of years ago and bought the bottom of the line mattress at a shop in the local rea. I believe it's 6" to 7" Queen Sealy. We then bought a 3" memory foam and placed that on the top and we've been good with it since we added the memory foam. It sleeps well and when I get up in the morning I don't have any backache. The replacement is a little heavy and the (new) lift cylinders have a hard time keeping the bed board raised.
Our ~10" thick, pillow top, home mattress on the other hand was recently donated to an acquaintance that does not have a good mattress. The mattress that we donated was a new replacement that we had just gotten on warranty a few months ago because the unit was sagging. This thing was killing us.
Our new queen mattress is a Restonic with the individually wrapped coils ... we're doing much better now. I can actually get out of bed and stand up without collapsing to the floor in pain.
The Restonic is almost as firm as the mattress in the motorhome. That said, I always sleep so much better in the RV.