I have a down sleeping bag and a down coat. Both are very lightweight, and oh-so comfy when the north winds blow. Down has the added advantage in that it typically lasts longer than synthetic substitutes, it is lighter and compresses more compactly.

But there is one caveat. If down get's wet, it's miserable and takes forever to dry. It's even worse than cotton. So I am very careful to keep it dry. Both items go into light weight stuff sacks, which I have lined with turkey roasting bags from the grocery store. These bags are super light weight, wear like iron, and are absolutely waterproof when closed off securely.

In 30 years of backpacking I have never gotten my down wet. But came close when my tent lost its waterproofing. Never had a problem with it until I got caught in a heavy and long lasting rain storm. But the turkey bag slipped over the foot of my sleeping bag kept it dry through the night. It was cold enough that I didn't have problem with perspiration soaking my feet.

I also line my food bag and clothes bag with the turkey bags. One other trick I like is a single merino wool underwear and shirt. Merino wool has the advantage that it doesn't collect odors. I just returned from a 5 day 4 night trip to the Rockies. Odor was never a problem. And merino wool has a wider comfort range than other materials. I have worn it hiking when it was 50-90 Fahrenheit and felt no need to add or remove clothing. My shirt is a long-sleeve T shirt so I just roll up the sleeves if it gets a little warm.