Our experience with "toppers" was frustrating in past campers. They caused us more problems than they were worth. They slide around, still felt the unevenness of the bed under it, and it made making the bed even more difficult.
After a couple sorriful experiences, we went the same mattress we had in the hosue ..... Serta. That is my advise.... whatever you have in your house, get the same in your camper.
Currently we have Helix mattresses. By far, not cheap, but sleep magnificent ... especially being 12 inches or more thick! The only problem, they are heavy and lifting the bed to access the storage under it is a 2 people job.
Bottom line ... what works in your house will work in the camper.