Today I went hiking in the mountains with Malamute, Duckling, and the dogs. The temperature was below freezing, but Duckling did just fine; he even took a nap in the carrier! Since we started doing winter hikes last year, we've found Determined Duckling to be quite cold hardy when properly bundled up.
The first year we took up snow hiking, we got a North Face snowsuit for Determined Duckling. It was pricey, but it did keep him very warm. When it got below freezing I layered his lighter snowsuit on underneath. (That one was a Columbia "Little D" dinosaur suit and it was just about the cutest thing I'd ever seen in boys' winter wear.)
This year, we spent far less on winter gear for the little guy, but got the same warm results. This year, I hopped on Amazon during the spring and ordered a snowsuit from a small company for about $30. It's a nice, heavy suit with a cute train applique on the front and has served him well. The only downside is that it doesn't have the fold-over cuffs for the hands like the North Face suit did, so we invested in a good, heavy set of mittens from REI.
The lighter snowsuit we kind of fell into by accident. Malamute got a $10 gift certificate from eBay in October, so we used it to buy a duck Halloween costume for $9 and some odd change. (We still have $.87 leftover, but there isn't a lot of worthwhile stuff you can buy on eBay for $.87.) When it arrived, we found that it was heavier and warmer than we had anticipated, so we've been using it as a light snowsuit ever since. He wore both his train suit and his duck suit today because it was extra cold. A quilt over him and the carrier for more warmth completed the ensemble and VOILA- toasty warm baby, even when it's cold out.