I would also like to have an exhaust fan controlled by both the shower light switch and a dedicated switch. Is a product (relay of some sort I presume) readily available that can accept two inputs to control a single output?
The main reason for this is it would allow the shower lights to have an independent switch next to the shower (IP rated if applicable). The other option would be to locate the shower switch on the same plate as the fan switch, and only allow the shower lights to operate if the fan were switched on, since that can be done simply by joining the switches.
For wall / ceiling lights in Zone 1 (above shower base), only need IP x 4.
There are LED strips that have suitable IP ratings, just need an SELV or PELV source.
Most cut-to-length strips will be constant voltage,so no "driver" as such & just need an isolating transformer.
Switching options are almost unlimited, but generally if the switches are reachable from in the shower they need to be IP x4.
Single & double UP-rated switches are available in most ranges of domestic accessories.
Some fans have built-in or add-on humidity sensor, giving automatic operation activated by the 'steam' from the shower.
I considered a fan with humidity sensors, but as this property is a rental and tenants never seem to clean extractor fans, reliability is a concern. Our dryer seems to run longer if I don't stick my hand down the hole and clean the damp fluff off the sensor. The simplest solution is to tie the extractor fan to the lights, which we will do if there isn't an easy alternative.