If you are adding the relay in parallel with a resistive load ( a light) you do not actually need any diode, the parallel load will do the clamping for you. I see 3 types of automotive relay. Those with no diode, fine for use with a switch. Those with a resistror across the coil, self clamping and usable either way round but with a higher coil current. Finally those with a built in pair of 30V zener diodes or a transient suppressor across the coil, so they clamp the excursion of the coil voltage.
Most are either SPST NO relays, though you do get SPST CO ones, but every time you want a DPDT you just use 2 SPST CO relays and parallel the coils.