buying new bed - divan - either a small double or double or King

I am 5ft 1.5 inches and about 11 stone. I find that firmer mattresses give me aches in my hip and shoulder and back ( I get back pain when I sleep on firm mattresses). I usually sleep on my side. I tend to like the feel of mattress compressing a little when I lie down. I have never slept on a Tempur or had a topper but would like try this when I buy new bed. What can you suggest in terms of spring tension etc?I wish to buy best for my money.