My first mattress topper was sheepskin, and it was just glorious in winter, but too hot in summer. I have since heard that I should have turned it face/fleecy side down in the warmer months. I then bought a microfibre topper which is like sleeping on a cloud; told a friend how wonderful it was, and she went out and bought a duvet very cheap in Sainsbury's and swears by it (used as a topper, beneath the bottom sheet). Anyone dubious about a topper could do a test run with a duvet under their bottom sheet for a night or two to see if they like the sensation.
Without a doubt, a topper is one of the best things I have ever bought/used. Remember the dictum, "Have the best shoes and the most comfortable bed you can afford, since if you're not in one, you're in the other".
Night night.