Last year I priced custom memory foam topper cushions for the boat at the Annapolis Sailboat Show.
After the defibrillator got my heart started again

, I went back home and purchased an
off-the shelf memory foam pad for a regular bed (can't remember if it was Queen or King size).
For the time being, we've been using it as-is, over top of the existing cushions. My wife plans
to eventually trim it to fit.
Anyway, this has made an
immense difference in sleeping comfort, and at a fraction of the cost.
I think we got a 3" pad, and it's adequate, but a 4" would have been better.