We have a beautiful size 2 BB that is way too big for my little one, Rosie. It belonged to her big sis Luma but she outgrew it pretty quickly. I held onto it for ages since I knew I would have another yorkie at some point but honestly, I'm starting to wonder if we will ever get to use it. Rosie is 10 months old and still being stubborn about growing. A size 1 is on its way in the mail right now
I would get the size three, but in the meantime you need to get a smaller harness that will fit properly. They can get their legs out of the BB leg holes quite easily if its too big, and then they can slip out. Very dangerous!