I have a shih tuz and a Lhasa. I had them berfore I got Remy. The Lhasa does not like Remy- he is a grumpy ole man
Bailey, the shih tuz, and Remy are best friends-- they play all the time. Bailey is very good with Remy.
I have a friend who has an older yorkie and got a shih tuz about a year ago. They are doing fine. But she does say the yorkie gets a little upset with the puppy play.
I think it depends on the personality of Baci. If you read up on how to indroduce a new puppy and take your time it should be a good thing. The balance for Baci is being a "only" child vs having another dog in the house.
BTW.. I love shih tuz!!!! Good luck