Hysson has a 1/8" Gossamer Gear Thinlight pad (cut to 36" long) that he curls up on. He generally cuddles up to my feet, keeping them nice and warm. (He is part of my sleep system!) If he's wet or if it's cold, I put a makeshift sweater on him made from an old polypro baselayer top. This has kept him warm down to at least 20 degrees. He carries both items in his doggie pack. Hysson is an indoor dog at home, so his coat isn't as thick as that of a regular hunting Labrador retriever that goes into freezing water to retrieve ducks. In fact, Hysson refuses either to swim or retrieve (the last because of his overbite--undershot lower jaw). He sure sheds a lot, though!
A short-haired, thin-coated dog needs a lot more warmth and should have a regular jacket, and perhaps a rain coat. My daughter's Vizsla (since deceased) needed both when out backpacking, plus a thicker sleeping pad.
The Thermarest folks used to make a sleeping pad for dogs, basically a 36" long Z-Rest. This pad was discontinued a few years ago. My granddaughter (age 7) now uses it as her sleeping pad. When I used it for Hysson, I had to carry it in my pack.
I like being able to roll up the GG Thinlight and stuff it in Hysson's pack, but he really needs something stiffer--several times during the night he shifts position and does the turn-around-three-times-before-lying-down act, which wads up the 1/8" pad. I may go back to something stiffer (maybe GG's torso-length Nightlite
), carry it in my pack, and let Hysson carry something of mine of comparable weight. A 30" pad is plenty long enough because Hysson sleeps curled up in a ball. At $16 it's considerably cheaper than buying a Z-Rest and cutting it down.