Hi Bunny1999,
The better online sources for toppers I’m aware of are listed in post #4 here.
There is also more information about choosing a topper in post #2 here and the topper guidelines it links to that can help you use your sleeping experience as a reference point and guideline to help you choose the type, thickness, and firmness for a topper that has the least possible risk and the best chance for success.
Phoenix