I would advocate no floor covering material other than sand, and rake droppings out at least daily. Make sure that the coop does not accumulate humidity, as it is much worse than cold. You really need not be overly concerned about extreme cold unless you keep single comb varieties ( which will get frost bite on combs) or small varieties of bantams.
You must have well ventilated coops, but the birds should not be subject to draft or rain.
Some whole corn in the feed is a good thing when the temperatures get cold, as they can use the additional carbs to help in maintaining body temps.
Be careful with birds that may be in heavy molt when the weather turns cold.