I think your plan will work just fine. I once bought a quilt that was torn in spots and generally in bad shape. I bought it at the time because I was making stuffed animal pillows with vintage quilts that couldn't be salvaged. Anyway, when I cutting my shapes out of the good parts I saw that there was a quilt underneath. After doing a little research I found that using an old quilt as batting was common practice during the depression era. People didn't have the money for fabric and batting. They used worn out clothing for piecing tops and old quilts for batting. Quilts were made for warmth and utility.....