First off, Welcome to YT!!! There are tons and tons of threads dedicated to people who are considering breeding. I suggest a quick search and read up on everything. Then there are a few questions you have to ask yourself:
-What are my reasons for breeding? Are they noble or are they selfish ones?
-Is my boy healthy?
-Does he have phenomenal qualities that the Yorkshire Terrier breed can benefit from?
-Do I have the $$ to do all the proper genetic testing that is required to produce happy healthy pups?
-Has he been tested for STD's?
-Has the bitch been tested for the same genetic soundness and STD's?
-Am I ready for the possibility of losing my little boy to him running away to find a bitch in heat?
-Am I ready to have a boy that will enjoy marking everything more than he does now?
I know there are more things you need to ask yourself, but I'm not a breeder and I answered no to ALL the questions, so my boy is neutered.
If you already answered yes to all the questions, then ignore my post and wait for an experienced breeder to come along and give advice.