Just be careful with a deep cushy topper. I love them, and a couple of years ago we bought a firm new mattress and a 3" latex topper. (My DH has back problems, so the idea was that the firm mattress would be good for him and I would have this nice soft topper.)
Everything was okay for a while and then I began to have back problems. Not DH, who already had back problems, but ME! Went to the doctor and it turned out I had two slipped disks in my lower back. I did physical therapy for months and things would be better and then worse.
Finally I realized that I was getting "stuck" by sinking down into the soft topper, and I was wrenching my back to unstick myself every time I turned. And I'm a restless sleeper, so that was a few times a night.
We yanked off the topper and put it away and now we just have a regular mattress pad. No more back problems for me. If I were to get another topper--because I do love that cushy feeling--I would be very cautious and try a one-inch topper. HTH!