I have a bad back too - and last time we bought a mattress we got a full latex one - i LOVE it!

The salesperson was terrific, and suggested that we get a sprung slat base instead of the normal ensemble base, for a little extra support, and now around 10 years later I still get the best nights sleep on it.

We also got a double sided mattress overlay, with one side cotton (for summer) and  the other side fleece wool for winter-  it makes it even better 🙂

Downside is it weighs a ton, but I wouldn't change back to a regular mattress for quids!