Range Extension: Xiaomi Mi Smart Home Gateway

I just bought a Xiaomi Mi Smart Home Gateway and I have Humidity/Temperature and Window Sensors installed in every room of my house.
Now it seems that the range of the ZigBee Network is not enough to reach every sensor in my house, in the farmost rooms the sensors are getting offline after a while…
Is there an extender for the Zigbee Network which can be used to boost/extend the network to reach all of the sensors? e.g. a second Home Gateway? Is there a separate hub to be placed as a relay station?

I tried to post that to Xiaomi International but they don’t seem to be responsible for that… Anyone experience with this?

Thank you

You can add another gateway or devices which replicate the zigbee signal (mesh network) for example the Xiaomi Mi Smart WiFi Socket - ZigBee Version (be sure not to take the wifi version).

Is this zigbee plug really a range extender?

Are there others too, which do the same job? I only need a range extender, other functionality doesn´t matter.