You dont need to use relays.
You can simply just use a DPDT (Double pole Double throw) switch.
If you can only get a SPST (Single Throw) switch you can connect the grounds (-) together and just switch the signal / (+)
Also, if you do use relays, make sure you use a power diode across the coil, when the power is released from the coil there is large back EMF ~200V that can do damage to the electronics