Have you considered using a blue flannel sheet? I use flannel sheets for quilt backs all the time and a King sized sheet would be large enough. Both Sears and Winners may have flannel sheets. I know Wal-mart has flannel sheets too but rarely seem to have King sized. I live in Ontario and Len's Mills is an excellent source for sheets but I know there are no Len's stores in B. C. My local Giant Tiger (small department store found in Ontario and Quebec) often has flannel sheets (seconds) for less than $12 and I pick up a bunch when I see them.