Answer Question
If you're going to be sleeping in 0F degree weather, then a -20F degree down sleeping bag would be advised. Anything colder, you should consider getting a -40 degree sleeping bag for winter camping.
Here are some really good down winter sleeping bags rated at least -20F (-28C)
Here are some super warm winter sleeping bags rated -40F (-40C)
Also two of the best sleeping pads to keep you warm when sleeping on cold surfaces in the winter are the Therm-a-Rest Z Lite Sol Mattress along with the Therm-a-Rest Neo-Air Xtherm Sleeping Pad.
What is the best sleeping bag for the Appalachian Trail?
What are the best Ultralight Sleeping Bags?
What is the best sleeping bag for climbing Mt. Rainier?
What is the best summer sleeping bag for camping in the Adirondacks?
Should I pack my sleeping bag on top or on the bottom of my backpack?
What is the best sleeping bag for climbing Mt. McKinley?
Are hand warmers good for keeping a sleeping bag warm?
What is the Best sleeping bag for camping in Montana?
What is the best sleeping bag for the Pacific Crest Trail?
What are the Best Sleeping Bags for very cold weather?