Several years ago, I covered the top of a quilted bedspread which was soft and warm. My son used it for years and this quilt saw the inside of the washer and dryer often.
If you are looking at polyester or acrylic, you might consider a light weight thermal type blanket for the wadding in your duvet. It is easy to sew twill tape to the inside to secure the blanket in place. My favorite find was a flannel duvet cover from the thrift store. I had options: duvet, quilt, backing, etc.
Part of the fun I have in quilting is to re-purpose items. I'm not cheap, I'm resourceful! :-)