To use a Raspberry Pi as the hub, you can use Home Assistant and a USB or GPIO Zigbee adapter such as the Conbee or Raspbee. Home Assistant generally requires a Pi 3. Automations are all defined within Home Assistant so they do not depend on having homogeneous vendors.
I usually go to Wire Cutter for this but their specific article is not really useful since they don't recommend any pure zigbee switch but only proprietary solutions.
For Zigbee switches, depending on your lights it could also be power plugs. Ikea and Philips are again the easy choices if they sell what you want. Depending on where you are based you could also find something that fits in your existing switchboxes.
They have a full list of specific supported devices here: https://www.apple.com/ios/home/accessories
The devices on the list that act as hubs also carry that support across to anything else they control; for example, the Philips Hue Bridge lets you treat a lot of Zigbee 3.0 lights/switches as if they were native HomeKit devices.
My parents have an apartment they rent and it's happened that guests forget to turn off the air conditioner at the end of their stay... It's not cheap to pay for that for multiple days not to mention that it's bad for the environment
I mostly want to do thzt because I want to be able to turn off heating and air conditioner remotely, but I would also like to have a master button to turn off all the lights when people live the apartment, a button to turn of lights on a path to the toilets in the bedroom and an alarm that automatically opens the shutters in the morning at the scheduled time (always found that waking up by sunlight is better)
Does anyone here have any recommendation of which devices I can control directly with something like a raspberry pi that's always on? I've read that Z-Wave's specifications avoid the Zigbee specifications pitfall that make them to vendor dependent..