You have a few options. You can keep your existing hub and simply run it on a serial to ethernet converter, or you can use a raspberry pi and ser2net to perform the same function as those purpose-built devices (one advantage is you can use the same pi for both z-wave and zigbee hubs). Or go with the list Francis pointed out.
One advantage of using the serial to ethernet option is you don’t have to rebuild your existing zigbee network. Migration details here Connecting to a remote Zigbee coordinator with ZHA using ser2net
Edit: the migration option assumes you run ZHA but I would assume Zigbee2mqtt would have similar migration paths.