My personal preference is 2 sets (in addition to the stock ones):
One set of the Weathertech Digitalfit Liners that I use all Winter. They absolutely protect the floor and sides of the footwells. Good protection, but they are just plastic, not very plush or comfy and definitely not luxury in appearance.
One set of very nice Lloyd's Mats for the rest of the year. So much nicer than the extremely chintzy stock mats. Much closer to what you would expect in a fine touring car.