Duvet covers can be very expensive in the dept. or linen store. I make my own using flat sheets from the discount store ($15 rather than $40 or more.) I sew the sheets together, wrong side out on 3 sides, add use velcro or buttons on the 4th side. The sheet selection is always better than the duvet cover selection - and you can put two different patterns/colors on either side to make it reversible.
To give new life to an old quilt that has seen better days, use extra bedsheets to make a new cover. We used plain white on one side and let my sons personalize it with fabric markers.