We live in Colorado.. where its currently 27 degrees. I put a coat on our pup before she goes out, because even all bundled up I'm cold standing out there for a few minutes! I can't imagine how chilly she is with thin fur.. we got our doggy coat at Target, of all places. I know theres some good online retailers too- perhaps some other DT'ers will be along with the sites! I cant remember.
Mine get cold easily. They do kind of forget about it once they get running and playing (or, Ripley does anyway... Keira's a bit more sensitive/dramatic), but I do have coats for them for colder days. They're much happier in their coats when it's cold out.
I figure if I'm cold so are they. I cringe seeing single coat dogs being walked without coats on.
That said if you order one online, make sure the place is reputable and that they will use signature confirmation, not just delivery confirmation.
Just passing that lesson on, as I paid $100 for a coat/pajama order back early Dec.(with someone well known) that was del conf only and am looking to be SOL it appears.
In the meantime I found some fido fleeces in a local store.