JJ, I got the topper at Herbergers. I think I've seen them at Target, too. Actually, I think most places have them by now.
Dotsie, we had a feathertop, too. It was really comfortable but after a while I had to "fluff" it every night because it got so packed down. It wasn't the best one on the market, but not the cheapest either.
Someone mentioned sheets for thick mattresses. When I used the feather topper I had a case for it, like a big pillow case - that on the topper and the duvet on the comforter served as our sheets. I kept a fitted sheet on the mattress and when it was time to change the sheets, I would just flip the feather topper. When both sides were soiled I washed both the cover and the fitted sheet. Sounds like a lot of hassle but it really wasn't and making the bed was a snap.