I have always advised on any RV related forum that when it comes time to replace the mattress in the camper, the best starting place for a new one is to get the same mattress you use in your house. (If you are comfortable with the one in your house).
We have always stayed with Serta's, but the last one we got was a Helix (about $1500 five years ago).
Note!.... if you spend a great amount of time in your camper, more than in your home, then don't cheap out and get an el-cheap-o mattress because you feel ... "It's JUST the camper. It doesn't have to be a good one or an expensive one." .... WRONG! You are sleeping on it and you are spending (approximately) 8 hours of your life (1/3rd) of your day on it. Why should you spend that much time on something that is not comfortable, causing you to wake up with aches and pains in the back, and feeling tired all day because you slept bad. No... get something comfortable, relaxing, and something that will truly give you a good night sleep. You will not regret it! (Neither will your back). And "expensive" does not always equal "comfort!"