Hi and welcome to Yorkietalk. I think you should be aware that we have an abundance of sickly dogs out there due to people believing that it's okay to breed just any dog. Once we domesticate an animal, it's very important for humans to stay involved in the breeding. When you take "natural selection" out of the process, you need to be aware how your decision to breed two dogs together effects the breed. Breeding is an awesome responsibility, and you should be responsible for every puppy you produce for the rest of their lives. Good breeders breed for the betterment of the breed, not for profit, and are responsible when they produce sickly puppies. Not every dog should be breed, and the first thing you need to learn is that a breeding dog is different than a pet. You need to buy it with that thought in mind, and work very closely with the person who sold you the dog, as she will be your mentor.
May I suggest you getting familiar with the Yorkie Standard, this site has a brief discription of standard, and you should study it in more detail, should you decide to be a breeder.
Yorkshire Terrier Club of America Official Breed Standard Some people call yorkies silky's but that's just referring to their coat; they have a silky coat rather than a cotton coat, and a silky coat is the preferred coat. There is another breed that is called the Silky breed, and they do look a little like a Yorkie, but the two breeds should never be mixed, it doesn't do either breed any good. I also suggest that you get familiar with some of the health problems associated with Yorkies, and learn which tests should be performed on the breeding pair.
Health Issues