Do yourself a favor and return the feathers now.
As has already been said, if your mattress/box springs are shot to hell you're wasting your money purchasing a topper. Purchase a good firm mattress and top it with 2-3inches of memory foam and you'll be good to go.
Someone mentioned heat retention in the memory foam. Yes, the memory foam is a very good insulator and your body heat will be transfered to the foam to some extent. How much depends on room temperture, your own body, and how much cover you use when sleeping. Do like I do and sleep butt naked with no covers. (hehe.... try to erase that mental picture..go ahead, just try)