We got our yorkie when he was a year and a half old and he still was not totally trained and made mistakes. He is now over two and go's outside (finally).
I found that if I kept him in a smaller area of the house and not give him the whole run of the house he learned a lot quicker. If I was in the family room I would keep him confined to that space with me or the kitchen etc. Where ever I was he was so to speak.Just so he could not sneak off and do it in a corner some where. If he had to go he would start to stand at the area closest to the door where he went outside. At first I put him out every hour like you are doing now.
Yorkies are hard to train and they seem to stay puppies longer than bigger dogs for some reason.. I had a yorkie for ten years and she never learned but I didnt know the tricks back then to train her properly so that was the biggest problem I believe.
Dont give up as you are getting into the final stretch and you will start to notice that he is not making as many mistakes.
You will have lots of support on this site to.Good luck with him.