I currently have a King Size Firm Mattress, and now find that I wake up I the night with aching shoulder joints, and hips. I believe that as I mainly sleep on my side, I should not be using a firm mattress. The mattress in being used on a metal framed bed, but not on slats. I have a base that has a solid surround, but is sprung. The depth of the base is 100 mm. I have been looking at some pillow top mattresses, but have just read a response you have provided to a previous online query, recommending that having a pillow top may affect the longevity of the mattress. You suggest using a normal mattress with a mattress topper. I am about 16.5 stone in weight, and am conscious that this does not help with the symptoms I have currently having. I look forward to receiving your thoughts.