First of all sorry for the belated post(busy day)…..
He weighs 25-28lbs
They make 'em to fit even smaller then Decker.....
I have an XS go to this link to look at their sizes.
http://www.ruffwear.com/Web-Master-Harness?sc=2&category=24

@basenjibratz:

Is it easy to put on? It looks like there are three snaps (buckles?). Does it go over the head? What about size? What size did you get your pup? It looks like it gives room for good adjustments around the waist.

1 After the initial adjustments are made it's a breeze to put on…....
2 Two buckles.... look below
3 There are 5 adjustment points makeing for a secure, snug fit.
@basenjibratz:

I would probably use it for a seat harness but I'm wondering if it's hard to get on and off them.

Taking the harness off…....

@basenjibratz:

Is the one that you have light weight? breathable mesh?

So light I was concerned the package was empty when the UPS dude handed it my way. :()

Not Mesh but still breathable….. we've been on several bike rides and he seems to start panting at the same point he did when not wearing it. Hence, no signs of over heating.

skippnr