The particular coat one chooses should be first a question of insulation (you'll need more the farther North you live), and second of personal style. If you are unsure where to start, you cannot go wrong with black; just find one that's warm enough for you. The coats sold in stores are usually only available in even sizes, since their appearance is less sensitive to fit than that of a bespoke suit. Nonetheless, many men choose to order bespoke overcoats, since this allows for a perfect fit with accompanying superior insulation. If your body type is such that off-the-rack clothes never fit you, overcoats are likely no exception, and bespoke will be your best option.