The petsmart harness was top paw brand, their harnesses go down to 8", most of the others only go to 10".
I bought the harness when Lola was about 14 weeks (I think about 2.5lbs) and it was a bit too big on the smallest setting, but that was ok because I didn't let her walk around in public anyway. She's about 5.5lbs now at 11 months. I'm not sure how big your pup is, measure him right behind his front legs.
This harness would work if you can find it in black (you can cut the rhinestone off)
Top Paw® X-Small Jeweled Comfort Wrap Dog Harness - Harnesses - Collars, Harnesses & Leashes - PetSmart
This is the right style but it only goes to 10"
Lil' Paw® Brown Plaid Leather Comfort Wrap Harness - Harnesses - Collars, Harnesses & Leashes - PetSmart
Hers is just nylon webbing with a pattern printed on it, a lot of their harnesses are double layered (nylon webbing with ribbon sewn on it) and IMO they're too stiff for a tiny pup.
Also make sure the seams aren't sharp.
Good luck!