I ordered the King size of the Luxury All Season Down Alternative Comforter even though I have a full size bed.  Judging from many comments on different comforters, I don't think most people realize that a down comforter in a duvet is meant to cover the top of the bed without much overhang on the sides or the bottom.  If you look at the measurements and compare them to the width of your mattress this will become apparent.  So I order up in size because I prefer the overhang and the overfill of the duvet, especially in the winter months.  It feels like a nice cozy hug.