Please take the time to go to this website and read about breeding.
To Breed or Not To Breed, Should I breed my dog?
I realize you love your little dude but just because he is cute and sweet does not mean he might be a good candidate for breeding. You also might want to see the over 1000 Yorkies that need homes now on petfinder.com and then also go to puppyfind.com to see how many people are breeding/selling these dogs. You need to be fully aware that millions of pets (including Yorkies) are being euthanized due to pet overpopulation so if you are going to breed your little guy you need to understand the burden you are carrying by doing this.
A responsible/reputable breeder will only breed for the betterment of the breed and this includes structure, along with color, temperment etc.