i have had maggie around a lot of bigger dogs and they typically do fine with her. the thing i worry about the most is the younger ones that use their paws to play...one swipe and maggie is done for. but an older one would probably be ok....you would need to see if this dog has been around other dogs before. labs are very good dogs once they are out of the puppy stage...and i think 3 years old is a great age for labs. they are gentle family dogs if they are brought up right. you really would need to look into the dogs history a bit but i think a lab or retriever would be a great addition to a yorkie home. under the right circumstances, that is
the only thing that concerns me is that you live in a small apartment. the only reason i say that is because my experience with labs is that they need a lot of exercise or they are destructive. the one we had, we did not have a fenced yard, and we never really were runners or went on long walks or anything. so she didn't get a lot of exercise. and she tore EVERYTHING up. it was horrible. we would take her outside to play and she would just dig and dig and dig. she stripped the bottom part of our big magnolia tree in the yard. she dug up carpet, she chewed door frames. and i know it was because she had so much pent up energy, she didn't know what to do with herself. other than that...she was a great dog. very easy to train.
I have always heard that labs are very gentle. Taylor was very gentle with people and most animals, she was very good with my bff's pet rabbit...but she was NOT good with cats. she actually shook one of our kittens to death. that was the breaking point for me. when my ex and i split up, he had to take her. i just couldn't bond with her after that. i was so upset...i had this kitten since it was born (the momma cat was a wild cat that we fed and cared for, as much as she would let me, and i realized she was pregnant..took her and the babies in). i LOVED this kitten and Taylor shook it to death. it was the most heartbreaking thing. but everyone told me that they couldn't believe a lab would do that and it was probably because she didn't get enough exercise. so i kinda blame myself for it. my ex wanted a lab sooooooo bad and i finally agreed to get one without researching what they required in regards to exercise.
anyway....i honestly think that for the most part, a lab would be a great addition, especially an adult lab. but it will depend on you and your living condition. he/she would need lots of exercise.