I'm using these relays: G6JU-2P-Y DC4.5
4.5v works well from usb power supply. if you have your own 5v supply and its a clean 5.0 v or better (even 5.3 is fine) then 5v relays are ok.
single coil latching. you pulse them one way, let go and they hold. pulse them the other polarity (switch leads) and they swap and hold the other way. neat little buggers 