Congradulations on finishing your quilt top! Can't wait to see it. Luckily you have some support to show you the next steps (sandwiching, basting, etc). I tend to prefer a complementary backing in either a muted floral tone-on-tone or depending on the top design, a fabric used in the top. Warm and Natural is my first choice for batting and luckily it is currently on sale at Joann's. Will it be quilted by you or someone else?