This is the harness I got for Jax after I brought him home. (Although I got black, not pink.) The extra small fit him from the time he was under two pounds, but it got a little snug by the time he grew to a bit over four pounds. He can still wear it, but since he’s gained a couple of ounces since his neuter surgery, I’ve ordered another one in small, in case he grows more.
https://www.amazon.com/PUPPIA-Intern...s%2C232&sr=8-4