as small as possible! I have good luck with electrical cords, the real thin lamp cord you can buy at the fardware store. Rip off the insulation and untwist and you have super-fine hair-like wire. Just get as small a wire as possible (bigger wire gauge number, like AWG 26+). Also, the wire for making your own circuit boards, wire wrapping wire, is very thin.
Almost anything you get will be too big, but something very thin will probably LOOK correct.
