I do not think you should rush to get him a 'buddy' just yet. He needs a lot of work first to help with his confidence.
I suggest seeing if there are Yorkie Meetups in your area first. Take a look at
Meetup: World's largest community of local Meetups, clubs and groups! - Meetup.com and see what there is to offer.
Next you need to do thing for him to build his confidence. There are a lot of great books out there to help you with this task. Help for your Shy dog (can't remember the exact title) but it is something like that and I am sure there are many others.
Teaching commands and tricks are some of the ways your build confidence. Even teaching "Give me a Kiss" can be done, and give lots of praise for doing commands.
Best of luck, but I do suggest you hold off on another little for awhile, your little fella has had a rough 3 years and he needs your attention first
