Poor boy... That t-shirt story makes me sad for him. I definitely wouldn't get him a playmate to stop him from being a brat
If anything, it increases bad behaviors because they have someone to egg them on!
I know my male really enjoys having a buddy to hang out with while I'm at work. I feel less guilty leaving him at home because I know he has his little sister to play with.
I would definitely stay away from that breeder though... Extra money because the pup was supposed to stay small? No way. Find a reputable breeder and you will be much happier.