Low power latching relay
Figure 1. A bistable relay. Note that A3 is common. Pulse A1 to switch one way and A2 to switch the other. The relay will remain in its last state.



Figure 2. A self-locking 12V single bistable relay module.

You might consider getting one with a second changeover contact. You can use this to monitor the switching action and switch off the changeover pulse when the changeover is detected.

Always keep your mains wiring well away from and routed separately from the low-voltage control wiring.