Ok, I'm all for having as many Yorkies as you can. More Yorkies more hugs, kisses and love. A friend will be a lot of fun for your boy. But please look at
all the aspects before adding another member to your household.
2 dogs = twice the food, treats and heartworm meds. Twice the time to groom, walk, train and play with. Twice the vet bills for annual exams and once they get old proper geriatric care.
Perhaps, for right now, doggie day care would be a good alternative for him to get out and play with other dogs. Or try to hook up with some other small dog owners in your area and do play dates.
However, if you decide on getting a second...please be sure to posts pictures of them having fun together.