I don't know when this happened, but the breed standard used to be 4 to 7 pounds. It simply states not to exceed 7 pounds now. 50 years or so ago in England there were 2 classes of Yorkies. Under 5 lb. class and over.
Crystal, I commend you on studying up on breeding before you actually do it. When I first bought a female to breed, I thought I had found a good breeder and mentor. Although my pups were very pretty and healthy, I discovered she knew less about the breed standard than I did, after I had spent some time reading and attending a few shows. I'm planning to begin again, and am still learning all the time. I suppose I always will. I was fortunate enough to end up talking alot with a wonderful woman named Terry Shumsky (now deceased), who asked me simply, "if you're going to put the time and money into breeding, why not do it right?" LOL. She was never judgemental, just very practical. Here's one big tip. If someone will stud their dog without asking for a brucelosis test, run. And a good breeder who studs her dog will supply you with one from her male. Protect your baby, and good luck to you.