Those of you that have one, is the sizing pretty accurate? What size is your dog and how big are they? I'm debating between the XS and the Small. Jackson is about 17lbs give or take, and has a girth of over 19". The XS is 1/2" width and 15"-21" girth. The S is 3/4" girth and 18"-22". I prefer the 3/4" width over the 1/2". But want to make sure it'll fit him. I really need a harness like this that is very adjustable, and I can get to fit him good, because he has a lot of different harnesses that I use for different purposes, but none really fit him "perfect". So I'm hoping the SureFit will!