It might be fun to have a "forum winter backyard campout".
Considering the temperature that you may be experienceing I'd like to suggest the obvious just to say it. Wear loose fitting wool socks, and have a warm soft pair of gloves just to wear inside your sleeping bag. NEVER expose bare flesh to the temps you will be in. After getting in your sleeping bag lay on your back and carefully layer your clothes - long underwear and fleece pants and fleece top of what ever should be carefully pulled down and up and interleaved for maximum warmth. If you need more - pull your down jacket over your sleeping bag over your torso and tuck it under your back which is towards the side of the tent giving more protection to your kidneys. Be sure to be very comfortable with your hood adjustments so you feel comfortable closing up - many people are cold because their heads stick out due to claustrophobia or fear of suffocation, or both. Get a small cuddly pillow - it will most likely have to go outside your sleeping bag not inside. A piece of fur over your face is nice when its really cold and a tent of course is much warmer than outside. And have lots and lots of padding underyou, like a 3-4 inch piece of open cell foam, so what if it weighs 20 pounds if you're on your back porch