This is the one I bought. If I was to do it again I’d maybe just go with one inch and spend some more money to get a higher quality one. But even this one made a huge difference in comfort.
I should mention as well that I had an old twin sized topper laying around that I used to supplement the queen. If you want the topper to cover the entire length of the bed you need to buy an extra piece. Also I have an XL camper.