To add some interest to the back I made a slot seam. I remember reading about this type of seam, I think it was in a Threads magazine, some time ago. It's not difficult to do. You sew the seam with a basting stitch, on the inside cover the complete width of the seam allowances with a strip of contrasting fabric, top stitch on the outside (the further from the seam the wider the slot but of course you can't go any wider than the seam allowance), unpick the basting and there you have a slot seam. I used this youtube video for instructions.