Joey's about 12 inches and he wears a size 3. We usually keep it in the middle notch, which really isn't very snug. There are 2 more notches on either side. Sometimes when he wears a sweatshirt hoodie with the harness on the outside we go down a notch. So I think size 3 should work for you. I looked at e-bay, when I was shopping for one, but it seemed like they had every size besides the size 3. Their prices were great and some even came with a leash. If you can't find one there, here's the link that had the best price when I was looking.
http://www.4weebeasties.com/index.ph...&id=7&Itemid=7 I can't tell you how much I love mine, it's so much better looking on a yorkie than the dogs they show.