First - do you have bits and pieces left from making the top? I love working them into my backs - more interesting and then no waste! But, if not, get a cotton that is 42 - 44 wide and you will need 2 pieces. They need to be minimum 60" (1 2/3 yd) equals 3 1/3yards. I would feel safer with 3 1/2 yards. The other thing is that while it isn't the best thing and can be a bit more difficult to quilt - use a twin bed sheet. If you have a place like Tuesdays child or Anna's linens(I know they are now closed), they sell single sheets. You can get a nice quality sheet in many different colors or prints for $5. Put the money in your top! p.s. on the same line, you can use flannel or certain blankets from the discount stores for the batting. Think about history, they used what they had. Unless it is an heirloom item, use what you have.