I recently bought a new memory foam mattress as the current one was almost 10 yrs old. I bought a double memory foam mattress as i had suffered severe back problems for some yrs. The new mattress was a 6 inch memory foam/foam combo costing £109.00. And although my back problems have not dissapeared this new mattress is far more comfortable and as a result have a much better nights sleep.
So although this type of mattress wont suit everyone,i would highly recommend it if your looking to replace your old one!!