If you can, buy a sleep number bed. We tried quite a few mattresses, toppers, etc., etc. We always had some problem with them.
We have friends, who have a sleep number mattress in their house. After hearing about how much they liked it, we bought one for the RV (they make an RV queen). It took a couple of nights to find our settings, but after that, it has been wonderful.
Be sure to read the manual. You will need to deflate it most of the way, while driving (to protect the bladders), but that takes all of 10 seconds to do.
We've now been using ours for over a year and love it.
Ben and Doreen
Home Away From Home - 2017 PT Crusader 315RST
TV - 2008 F250 Lariat 4X4 6.4 Diesel
42 nights camping in 2015
61 nights in 2016 (still not enough!)