Just be careful if you get a Yorkie that you find a good breeder. Don't go to the newspaper or anybody who doesn't show their dogs in conformation. Yorkies are among the most common dogs for backyard breeders and puppy mills, and if you get one from a shitty breeder you will have a neurotic, unhealthy little mess.
Don't buy from anyone who describes their dogs as "teacup" or anything else gimmicky. Don't fall for the "Oh, we only breed our dogs as companions" bullshit. Find out what kind of titles and health testing the parents have. Don't buy from anyone with more than one or two litters on the ground at any one time. Be very leery of anyone who breeds more than one breed. Do not buy from anyone who sells crosses (yorkiepoos, schnoodles, whatever). Don't buy from anyone who will not let you see their breeding facilities.
Most reputable breeders will offer some kind of health guarantee, and by that I don't mean "Oh, if it gets sick I'll just replace it!" They will require puppies who go to non-showing homes to be spayed or neutered by a certain age. They will have a clause in their contracts for you to return the dog to them if it ever needs to be rehomed. Most importantly, they will be able to tell you what their particular breeding program is doing to improve or maintain the quality of the breed.
Anyone who doesn't pass the sniff test is a backyard breeder or a puppy miller. Don't support those people. They are the reason purebred dogs have a reputation for being miserably unhealthy, and many of them will try to sell you what is basically a vastly overpriced mutt by claiming it has "hybrid vigor" - this is a lie. If you take two purebred dogs who have inherited hip problems and breed them together, their puppies will have hip problems. They are also largely responsible for the huge overpopulation problem facing the United States.
A well-bred Yorkie from a quality breeder will usually live to be seventeen or eighteen years old without any major health problems and be a calm, easily trained, pleasant companion. Conversely, a Yorkie from a crappy breeder will likely be neurotic, undersized (since small is cute), miserable wreck whose patellas will luxate by the time it's four or five years old and require expensive surgery just to not live in constant pain and be unable to move.
Anyway. I'll get down off my soapbox.