I would not buy an over-size pair of shoes just to fit thicker socks. If you want to get winter shoes, that's fine, but simply getting summer shoes a size bigger is kind of a waste.
Generally, the warmth scale goes:
Toe covers -> shoe covers -> booties -> Winter shoes
Shoe covers and booties work best for occasional use, since they can get torn up a little walking around. These are best for using 10-20 times a year. If you're going to be using them every ride from Nov-Mar it's potentially worth getting a dedicated pair of winter shoes. In that case, you probably want SPD for easier walking, and just pedal swap in Nov.