I've been wanting a simple white duvet for my favorite down comforter, but didn't want to spend a ton of money on one. Solution…flat white sheets. I use them for just about everything.
Just cut the sheets a little bigger than your comforter, stitch three sides and add some simple ties made from left over scraps for the open end.
Super simple and a lot less money.
I would suggest cutting the sheets to size as opposed to tearing them. I tore mine and they didn't tear straight. I ended up having to trim each side to even them up. It would have been much easier to cut them in the first place.