If your existing pup is a male, then the best playmate for him would probably be a female.
As a general rule (of course, there are exceptions) opposite sexes are the combination most likely to get along. Two males is the next best, and two females is last.
I would, however, suggest that it is better to wait until your puppy is at least a year old, or better, 18 months before adding a second dog. He'll soon be entering his adolescent phase - and would really benefit from your undivided attention during those months. If you wait till he's through it before adding a second puppy, then he'll be able to help you train the baby. If you get a second pup now, you'll have two babies on your hands (or worse - two adolescents).
Or, you could think about adopting an older dog (older than 18 months)
