Air mattress solution
To start, we have a small Hummingbird 17FD which has a short Queen side to side and a dinette that folds into a standard size short "full". I bought a hybrid spring / foam mattress to replace the factory queen, Visgantti from Amazon. It's okay as I don't spend 365 nights a year on it. We both get up at night so I opted to take the dinette. I turned the dinette into a full size bed and put a 4" blow up mattress on top. I get the best night's sleep I've ever had with the blow up on top of the cushions. As a caution I have to say it does squeak if you toss and turn a lot but it's the closest thing to a sleep number mattress you may find. We can use the dinette during the day and easily turn it into a bed at night. I am 6' and weigh 240. 79 years old. I bought a Zinus Green Tea Mattress for my home. Zinus is the hardest mattress I've ever slept on and I've had a back ache for 2 months. Make sure you can tolerate the hardness of the Zinus before you buy it. It's rated medium firm. I have a 3" memory foam topper on the Zinus so I don't wake up in pain. Good luck with whatever you choose.