Memory Foam Mattress
 

We just installed a 5" Lucid Memory Foam Mattress over the top of the sofa in our 2310. It turns out the sofa in a 2310 is almost exactly the size of a Full XL mattress--a size we didn't even know existed! There's even bedding available in Full XL. Who knew? We haven't spent the night on it yet, but it seems firm enough for our not unsubstantial size, but soft enough to accommodate our achy old bones. At a $140, it is less than many of the memory foam mattress toppers we have seen, and certainly less than a custom mattress. And it only weighs 26 pounds.

https://www.amazon.com/LUCID-Inch-Me.../dp/B00NX8GDSE

Memory foam mattress
 

I think you will like the comfort level this set up gives you. Keep us posted.