Gram, whether you are making this back to be quilted by a longarm quilter or you on your DSM, you do need 1/2" seams in the backing - for some reason they lay flatter then a 1/4" seam...and don't use the selvedge in the seam as it has no stretch and the rest of the fabric does. As Judi said, make the back asymmetrical - much more interesting and so much easier!!!