SPDTs can be momentary or bi-static, depending on the switch. If your existing SPST switches are momentary, then you should replace them with momentary SPDTs (w/o center-off position). Twisted pair wire can be purchased, but it can be made from two separate, insulated wires with a simple jig that employs a pair of fishing swivels (one per wire in the pair) fastened to a short bar (wood, metal, plastic.) The swivels allow the wires themselves to not twist while wrapping around each other. You clamp one end of both wires together to the edge of a bench top, etc., and connect the other end of the wires to the swivels on your jig. Now, start twisting the wires together with the jig in your hands. You could even put a screw through the middle of the bar (between the two swivels, but on the opposite side of the bar,) then chuck that screw up in a hand drill, and let 'er rip! Twisting insulated wires together increases their mutual inductance, without adding overall inductance. This helps reduce any generated noise from emanating from the wires, as well as reducing the ability for external noise to couple onto the wires. Direction of twist does not matter. In a pinch, zip cord (like used for small appliances) will work too, even though it is not twisted. Just keeping the signal and return wire uniformly close together over the distance spanned helps.