Greetings,
You could also look into adopting an older yorkie (1+ years old). Stay away from those who purposely breed "minis" or "extremely tiny" style of Yorkies (1-3 1/2 pounds). The Yorkie breed profile reads basically 7 pounds and under. There are those that do exceed that weight just by accident. The breed long ago was set around 22 pounds, in case you're interested.
They will get along with another dog, especially if your GR is as good natured as the breed is supposed to be. If you get a bitch, it will be natural for her to rule the roost, no matter her age, especially being a terrier. :) But if she's already an adult, you won't have to worry about injuries to a growing pup whilst they play.
hth and good luck
toodles