Welcome to Pet Talk!
First off, I would until the puppy is at least a year old before you decide to bring another dog in. That way, your black lab would I'm guessing have some sort of training already, and you wouldn't have to work with two young puppies. Also, two young pups might bond close together, and could "push you aside".

That being said, maybe try going to the animal shelter and seeing all the wonderful dogs there. Or, you could go with another lab.