You can use almost anything you want as backing - you area making the quilt, you get to make the decisions! Having said that, be warned that some fabrics are a bit harder to work with. Fleece and minky like to slip and slide around A LOT. You need to be even more careful about puckering and gathering. Also, there are many, many online fabric stores. This group can give lots of suggestions and then just watch for their sales (watch their shipping costs also). Any, you can always buy online from the 'big' places like Jo-anns, buying the sale fabric and use their free shipping coupon. Welcome, have fun quilting and remember, you are the boss!