I sew about like you do. I usually get about 2 yards. If I think it might be a border I buy three. But last night I was digging through my stash for border fabric, and found 2 perfect ones--grrrr both 2 yards. I needed 2 7/8. I did find one 3 yard in the same colorway, but not my first choice.
I usually get my backing fabric on eBay, because I can type in "blue quilt fabric 6-12 yards", and come up with more than one choice (usually) on sale. I have been an eBayer for over 13 years and in all that time I have had only one problem and eBay returned my money and my postage within 24 hours. And I got to keep the fabric which was quite pretty. The people that I choose to buy from have small shops, they just have them on eBay instead of a website.
My stash, which I just about doubled last week by cleaning out some project drawers, is in bad shape for lights. At the moment my lights are mediums, so next month, when the money rolls in, I'm hoping to first in line at the LQS.