way to go, m-fay, can't wait to see your quilts.
But you may need a bit more than 6 yards, I remember I bought 6 for a queen, and don't remember how much more I had to buy. It wasn't much but 6 didn't do it. I guess what I am suggesting, is don't buy your backing until the top is done! I just check my cheat sheet I had found someplace and they said 7-1/2 yards, but that seems excessive. But then, some people make a more generous queen than others.