Pocket sprung mattress on Tempur ottoman base - advice please?

We have a king size, slatted, Tempur ottoman base and wondered what mattress would be suitable as a replacement. We are considering a pocket sprung mattress as the current Tempur mattress now needs replacing after 9 years and we are both experiencing back ache from it as well as being 'too hot' during the night.
Please could you advise? Thank you