I bought a Novaform ComfortLuxe® Gel Memory Foam Mattress Topper from costco for 99$ last year. Used 1 year by clean female graduate student. non smoking no pets.

http://www.costco.com/Novaform-ComfortLuxe%C2%AE-Gel-Memory-Foam-Mattress-Topper.product.100115178.html
Comes with white washable cover

Selling for 30$ OBO 8/14/16

Pick up on Stanford's campus.