I found out after numerous tries that you should never go by size. Different manufacturers have different standards. I found out the hard way. That's when I started buying from Barking Dog Clothes at the suggestion of a fellow YT member. You give them your baby's exact measurements and they make to order. You can select style, color, fabric, even embroider name/sayings, all for free. Free shipping also. The price is also excellent. I received my first order a few weeks ago and cannot be more satisfied. You should give them a try. Here's the website
dog clothes