I get flat sheets from Walmart. I find the cheapest storebrand and they are packaged individually so I don't have to buy a set. The cheapest have a fewer thread count and are more like quilt fabric. I even found a decorator line with bright colors that perfectly matched a bright aqua that I used for my DD's quilt. I hand quilted a queen size before I "knew better". It seems they were around $6 or $7. If I were trying for a competition quilt, of course, I would spend a lot more for backing. The other advantage of the sheet is that I don't have to be so worried about seams being straight. I always find that difficult with batting sticking out around the edges before I trim it.