Try Kingsdown brand, Emerald Crown model. I bought one for the guest bed which is in my sewing room and LOVE it. Not too firm, not too soft. I have a bad back and did I say I LOVE it. Often fall asleep there after sewing instead of going to my bed which is a Sleep Number. It's half the cost of Sleep number too.
Kingsdown Emerald Crown. Bought ours at Sleepy's.