You won’t need a separate range extender. For both zigbee and zwave, pretty much any mains powered devices except smoke sensors will automatically act as repeaters anyway. The most popular are usually light switches or plug-in pocket sockets, but also in wall micros, plug-in sensors, plug-in sirens, etc.
Battery operated devices do not usually act as repeaters.
Z wave repeats only for Z wave and zigbee repeats only for zigbee, so just take that into account when deciding which devices go where.
For more information, see post 11 in the following thread (the topic title is a clickable link), then go back up to the top of that thread and read the whole thing.
