I am too lazy to go back and look and see if I already told you about Park Avenue harness.
None of mine can wear puppia. 1 wears XS ipuppyone which has an adjustable neck as well as chest really well. 1 can still walk out of it and on 1 it is still really big.
Park Avenue are made to measurement and mine fit perfectly.
My 11 month old weighs what your baby weighs (right at 3 pounds) and my other two are 14 and almost 15 months and are 3.5 pounds so I know that these will fit your baby.
Here is a link:
Designer dog harness, small dog harness, dog walking harness. -
Ordering can be confusing so let me know if you choose to and I can help (others here can, too-they are the ones who helped me!).