A larger Yorkie would be less fragile. However, a word of advice: the Yorkshire Terrier breed standard for size states that weight should not exceed 8 lbs. This is useful to know to prevent yourself from being duped by unscrupulous breeders into buying a dog that can never be bred or shown.
For more info on the Yorkshire Terrier breed standards check out this site:
http://www.ytca.org/
This is also a great place to find a breeder in your area. Email some of the breeders listed there.....they should be glad to answer your questions!
Good Luck!