To add ZigBee sensors to the network we need a bridge, the one that keeps popping up is zigbee2mqtt. This is a USB based solution that is plugged into an existing PC or Raspberry Pi. Which is probably okay for my scenario as the Pi is at one end of the house and the server is centrally located, so will probably give enough coverage.
There is also the option of making it into a ‘router’ – a standalone repeater, or can be connected to an ESP8266 to form a serial socket over WiFi to the Home Server.
The development kit consists of: