It’s like Bluetooth but for smart home devices.

If you have Philips Hue devices they support it out of the box and are ridiculously easy to use with Home Assistant. A bunch of others do too

I’d recommend you use the Home Assistant OS and also set up Zigbee2MQTT.

As an alternative to your smart switches, you can use the Hue wall switch modules, which you can wire to any wall-mountable switch/button and link to anything.