I'm in the process of buying a new motor home. We have traded in our old motor home and we are waiting for our new MH to arrive. Our new MH will have the air inflatable bed. I didn't know that I needed to deflate the bed when traveling through high altitude.
Our old MH had a spring mattress that I could not sleep on. I tried a 3" memory foam mattress but I still had trouble sleeping. I found a business on-line that sold foam. I bought a 6" foam pad to my dimensions and the I replaced the spring mattress. The 6" foam and 3" topper worked great for me. I slept great. My foam solution is cheaper and lighter than a named memory foam mattress. My gas struts were just able able to accept the added weight.
When we traded in our old MH we kept our foam mattress just in case we can't sleep on the sleep number bed.
If you decide to buy a 3" or 4" memory foam memory foam mattress topper and need to trim it to short queen size, the trick to cutting the foam is an electric knife.
Safe travels. JD