Hi Misskira,
It can be almost as difficult to decide on the “best” topper as it can be deciding on the “best” mattress because it is usually a blind purchase that you can’t test the combination ahead of time. There are some guidelines and sources linked in post #2 here though that may be helpful.
Brooklyn Bedding (the manufacturer of the Dreamfoam mattresses) sells toppers as well that have a 120 day trial period for exchange or refund (less return shipping costs).
Phoenix