You could buy a plaid that is printed on the bias. It would lend visual interest and you wouldn't have to worry so much about keeping lines straight.
I just wanted to pass a tip along - one of my favorite ways of adding sashing to a quilt is to sew strips of sashing around each side of every block. When you assemble the rows into a top, all you have to do is make sure you match the seams. I find this much easier than sewing on long strips of sashing, then trying to make sure all the blocks line up exactly even.