Typically I do the lightweight baselayer + lightweight down + shell for all of my layer for needs, but I'm a boulderer and in the winter I can't be bothered stuffing my layers on to rest before I take them off again for another burn.
I'd like something warm and cosy, don't care about waterproof and weight isn't a major concern given I'm lugging in pads anyway. I want to be as warm as possible on a cold, windy winters day from just one layer I suppose. Without spending a fortune on some sort of everest base camp onesie...