Note that Zigbee relies on a network mesh so using three or more lesser good Zigbee Router devices will generally be better than using just one great Zigbee Router device. Anyway, here are suggestions:
Good = “IKEA Trådfri Signal Repeater” or “AEOTEC Range Extender Zi”.
Great = Sonoff “ZBDongle-E” or “ZBDongle-P” - flash with Zigbee Router firmware & use USB-chargers.
Tip is to have at least three stable main-powered Zigbee Router devices that are always on.