I have a 4 pound yorkie and my parents have a much larger Shi-tzu. They LOVE each other.
My grandma has a 6 or 7 pound Yorkie and a 9 or 10 pound Maltese. They are truly the best of friends. What's nice is neither of those breeds shed.
Shi-tzu would probably be a fine choice, or you may consider a Maltese as well.
