When the Santa suits and wigs begin appearing in stores at Halloween, that is the best time to think about purchasing one to use in two months. The best quality outfits will be reasonably priced, and have better accessories, including the wigs.
If you wait until a few weeks before the actual holiday to purchase Santa suits and wigs, you might find that only the cheaper suits are still available. Even if you find quality outfits, you may have to buy the wig and beard separate, if you can find them. You want to choose one that fits, above all.
Velcro closures will make it easier to get in and out of it, but wear out quickly. Zippers are a good alternative, especially if you use padding. Read the label on any wigs, and choose one that uses mostly human hair, if you can find one, to avoid allergic reactions.