I love all the quilt backs! Great job ladies!!! I did a pieced backing for my niece's quilt a few years back and loved it so much now I plan to piece them. It adds such great interest to the whole quilt. Of course I think it should relate to the front in some way.
I never thought of looking for a board of quilt backings on Pinterest. I'll have to go look now.
How I center my backings and tops before quilting is with toothpicks. I fold 2 of the round type in half and make a 90 degree angle (corner) out of both of them. Put the 2 corners together so they form a + and use painters tape to tape them to the bottom of the backing. When putting the top on center it up by feeling for the toothpicks in the center and they line up perfectly. I'm always within 1/8" and no issues. Love using my toothpick method.