You are best off using a jeans needle — size 80 if the denim is not heavy, size 90 for thick, heavy denim. You could use regular needles in those sizes too, but jeans needles have a sharper point designed specifically to penetrate denim easily. Schmetz brand needles fit most modern machines. The store where you bought the machine will know and, if they are a dealership, they should also have the needles in stock.