Assuming this is more about comfort than pressure ulcers (and maybe even if not), I would try an overlay on top first, Vince. A standard hospital bed mattress isn't likely comfortable for anyone. Latex is a good option for many people -- three firmnesses, various thicknesses, pretty cheap on Amazon and the like. We've done threads before, but check out the Pure Green brand. I'd suggest a foam pillow (which are also available in latex) as well, as conventional pillows probably aren't supported enough for you.
Also make sure your arms/elbows/feet are well-supported and your hips are aligned, as that contributes a lot to back and shoulder pain if they are not.
Best,
Laurie