Now-a-day Memory foam mattresses is very popular in market. These mattresses are made of layers of different
densities of foam that respond to weight, temperature and are known for comfort because it is especially shape of your body from pain.
Normally back pains are caused by too soft a mattress.
Since it is memory foam, it may not work properly if you top it. The mattress needs to form to the shape of your body. I have a memory foam pillow and it took about 3 weeks before I could honestly say it was comfortable. Now it is great. You could put a wool underlay on it though.
I just bought a full sized memory foam mattress and considering that it's medium firmness and I have back pains from my previous mattress I was wondering what I should buy to layer on it for more comfort.