[LunarBerry]

I agree with everyone here, you would want to breed for the better of that breed, not 'just because" and there's a very good reason for that. So many health issues can happen, even with some of the better breeders. May not be with your litter but if you sell to someone else later on or give your pups as a gift, they may decide to breed them and then the cycle goes over and over again, and they may not do the right thing by the yorkies, whether they realize it or not. You need to know that it's both time consuming and costly to do it right and proper, even if it's for yourself/family.
You also would have to take great care in who you decide to sell/give to and look for red flags, if you truly care for your pups. (you could easily get 3-6 in a litter, so it's not practical to think you'll breed him for just one companion "daughter/son")
I'm not a breeder, but this is something I can truly appreciate as a yorkie lover. I believe it would be best to find a companion elsewhere, adoptable or from another reputable breeder. Older dogs are great companions as they are already fairly set in their ways so you can have a better time figuring them out and if they'll fit with your lifestyle.