This is kind of a messed up time of year, temperature wise. It's tough to know what to wear when it's -5 and dark in the morning but +5 and sunny in the afternoon. For some reason that 10 degree temperature range feels far more significant than, say, the difference between +15 and +25.
Of course that's why layering is so important. Not only does it provide extra warm without a ton of bulk by creating warm air pockets between layers but it also allows you to adjust your warmth easily as conditions change.
The Mountain Hardwear Microgrid Jacket is a perfect example of apparel that can be worn alone or as a base layer. It has a reasonably snug cut to allow for overgarments but it's not clingy (the ample stretch of the material likely has something to do with that). It has a hem draw cord and 3 zipped pockets, 2 for your hands which are warm enough to keep them from freezing in temps a little below zero.
For $120 you can add this garment to your personal wardrobe and literally establish the base layer of your plan to tackle the winter temperatures to come.