They are awesome little pups; but, if accidents in the house are a deal breaker, I would suggest you think about another breed. They are not impossible to housetrain, but they can be difficult. Some people swear they have perfectly trained yorkies, bless them as I have never had one that was "perfect". Some better than others, but then, I am also not totally upset when they do mess in the house.
Consistency and positive reinforcement are definitely key but they "can" still be difficult.
I could go on for days about the good things .. they are, as I said above, awesome little pups!
But...you wanted to know about the housetraining and I think if it is that important you need to rethink.