At the end of the winter shopping season, go into stores like Sears, Penneys, etc. and buy flannel sheets. These are generally sturdier than what you find in WM, JoAnns, etc., and, when on sale can be an extremely good buy. I've used them in a couple of quilts with good results. The bonus is that you can include a matching pillow case with quilt - no extra work on your part.