Relay Recommendation (Zigbee)

Hello,

I’m pretty new to HA but I love how everything is working so far. I’m running Z2M.

Now it’s time for the bathroom:
I’m not able to use smart bulbs, so I was thinking about using a relay which sits behind the wall switch.
The switch is 2-bay - one is controlling the mirror lights, the other one is controlling the ceiling light + the exhaust fan (that’s why smart bulbs wouldnt work because the fan would be always on)

I was wondering what kind of relay I would need because of the cables and the limited space (about 1cm of clearence in depth) and how the setup would look like.

Any recommendations?

Greetings from Germany
Simon