Warm and Natural batting you have to quilt 10" apart so you will need to add quilting to your squares if you opt to use this brand. A twin size will be sufficient for your quilt. You will have leftover.
http://www.warmcompany.com/wnpage.html
Quilters Dream Poly and Dream Green are the only two batting products on the market that I am aware of that allow you to quilt as far apart as 12"