If you do get one, pls don't get the shock collars.
I have read they now have some that emit a high frequency sound and others that spray a whiff of citronella. At least that does not sound quite as bad as shocking the poor things. I have never seen them used though, so who knows they might be just as bad. Just a thought.
So far, I have always been able to train them to limit barking -- they take reminding often, but they will stop when I tell them.
Is it just the lab mix that makes your Yorkie bark? If so, is there a way to keep them separate?