They do say you should buy a new mattress occasionally.  Yesterday we splashed out an enormous amount on a new mattress, with springs and memory foam.  It is comfortable and bouncy.  We have to wait a few weeks for it to be ordered and delivered.  We also bought a new synthetic duvet.  Two actually, you have the thin one in summer, the thick one in spring or autumn, and both in winter.  It is only the cheap one from Argos, but it is fantastic.  My other tip is to put a king-size duvet on a double bed, so that it hangs over the edge of the bed: John agrees; he has woken at 3 in the morning to find me wrapped up in a smaller duvet.