Borders might 'stop' the eye but I don't think they are totally necessary. If you have no yardage from these fabrics I would simply pick something that blends well and go from there. For me, I try to find backing fabric that incorporates some/all of the top colors. And I usually try to pick the least common/noticed fabric in the top and find binding fabric that will pull that color. Just me. It's a beautiful quilt and your mom did a great job. Might be a nice 'hug' for her when you get it finished.