I use my walking foot to quilt all the time. I find free motion too stressful, especially with a bed-sized quilt. The first thing I would do is use some wash-away thread to anchor the quilt - stitch straight down the middle each way. Then your easiest options might be to do a diagonal grid both ways, or to stitch straight lines across the white/black spaces up and down, or to stitch very gentle curves across or down. I highly recommend Leah Day's book "Walking Foot Quilting" - it will give you confidence. After you finish quilting and binding, wash your quilt to get rid of the anchor stitching.