I have a bunch of days off the week after T-giving (27 Nov-1 Dec), and was thinking about Paris. Will the decorations be up then, or don't they go up till later in December?
There's nothing that really makes it "Christmas Season" so individual places make their own schedule for when they put up decorations. You'll be on the cusp on having everything Christmas out. The department stores should be decorated then, most of the major Christmas markets will have started (not sure whether they'll be full-blown by then), but some of the smaller, neighborhood stuff won't be up until the first weekend in December (the 3rd).