I'm sure there Is considerable debate about this, but I do remember reading about standard thermal header wrap NOT being a good Idea for the sills. I'm not sure why since In theory the wrap should keep a lot of the heat from escaping to the sills but I have definitely read about Issues with It.......perhaps associated with wrapping the cats....they may get too hot for even the thermotech wrap.
Another idea is to get the aftermarket sills and vent them (see a post from Dave 6666 on this from a few years ago), and save your OE sills for resale if you ever need to sell the car.