I have a fairly new mattress, about 6 months old, from Amazon - my old one was saggy as anything and my back was in bits from it. This one is solid as a rock and I love it BUT it's tufted and the dips where the tufts are are huge and I always end up in one in the night so my back is starting to hurt again! I don't really want a mattress topper if I can help it as the mattress is already really thick so I don't want to add to the height. Is there such a thing as a firm mattress protector so it makes the surface more flat??