My husband had purchased a really nice, warm comforter before we met but it was ugly, as in black on one side and gray on the other. I bought two high quality light blue cotton king top sheets and made a duvet cover for it. I used the top hems for the bottom of the cover and put buttons and button holes in them to close it up. To keep this heavy comforter from shifting inside the cover, I placed a few ties along the top and down the two long sides. Now, nearly 11 years later, we still sleep comfortably under it every winter. You could probably use the same (or similar) idea to make it reversible without using batting.