I would not ever get another cat while I have a yorkie. Chewy and Sadie drive my older cat Oliver crazy... they love to chase him. they don't fight but the chase and bark and Oliver spends a lot of his time on chairs and places where the dogs can't reach.
It's crazy because he is so much bigger but he runs away and they love it because then the chase is on. We spend a lot of time trying to get the dogs to leave my poor cat alone.