Same situation here...We have a husky and morkie and they absolutely LOVE each other. the husky is older by about a yr and when we brought lily home skye (husky) was in love with her from the start and vice versa. we moved to Japan and couldn't bring skye last minute because her microchip was defective (ughhhhhhhhhh) so lily was alone when we got here and she looked really depressed and home sick so we thought another puppy would help her so....we got Taka (yorkie). Lily really cant stand him because he will not let her sleep! lily will play a little bit with him until he starts jumping on her then she gets angry and finds somewhere where he cant go and sleeps. its kind of frustrating because we were hoping she would play with him but that wasn't the case so now i have to watch them to make sure lily doesnt snap at him. She has become a meanie pants since we got to Japan. My reason is because she misses Skye as do we
since your puppy is only 4m old he should be fine with a playmate!! i say go for it!!
sorry for the venting lol