Hi, sdkachif!
I believe, there's no such thing like an ultimate solution. As alophysio already mentioned, it depends on weight of a person and preferred sleeping position. Generally our advice is to have a medium firm mattress with a high spring count. A soft pillow top can be useful if you/your patient are particularly thin or sensitive in your/his/her bony areas.
For instance, before and after surgery, I found a firm bed with a foam overlay is best to sleep on. You need that softness but you also need to be held firmly, level and straight.
So if you're the one who is choosing the mattress, you really should go the the nearest good bed store you can find and try them out and not just lay down and then get up. Take your spouse or a caregiver with you to assist you if needed.