My brother, mom & I have sibling puppies weighing 2.8, 3.5 & 4.2. We had a really hard time as even the smallest sizes were too big and the closure would often catch in their fur. We found these adorable shirt type harnesses that velcro so they can adjust, come in different sizes, prints, & you can even get matching leashes. My avatar pic has one, and my album has one of Ellie walking with the leash too.
Our babies absolutely LOVE them! Here is the website.....
J & R Painting and Crafts - Pet Stuff