The dynamics of your discomfort-warm enough initially, foot discomfort later-suggest that nutrition/and hydration issues may predominate. Your feet are at the end of the circulatory line, and tend to be the first place that shortage of fuel and fluid show up. Winter camping requires high quality, purpose-designed equipment, or a very old-fashioned approach. A tiny snow-cave, lean-to or pup tent may be more comfortable than a large and airy 3-season tent, wool blankets and woolen clothing may prove superior to multiple layers of summer-weight synthetics. Whelen and Baker tents are designed for cold weather use in combination with a fire, and the kifaru folks have amazingly light tents and tent stoves. A tepee, yurt, or cave will accommodate a lot of campers and a fire for cold weather applications. Folks have been living rough in the cold for thousands of years, and the technology is there to make it a comfortable experience: but it is the not the technology of synthetic, ultra-light, inexpensive big box retail outlets that does so.