Wrong answer.
Adding more devices to the mesh WILL extend the mesh network. Like the TS said:
What kind of devices u have at this moment and how many?
Making a good mesh network starts near Homey and then every few meters another non-battery powered device. Just putting 1 in the bathroom is not always a good solution.
I have like 50 Zwave devices of which half of them are non-battery powered. The first 2 devices are like 20cm away from Homey and have a total of like 9 on the ground floor. 2 of them being near the stairs in the hallway. In the corridor one floor up there is another plug along with 3 Fibaro switches/dimmers. On the second floor, near the stairs again, there are 3 plugs again. This way i can have several battery powered devices reaching Homey all the time. So don’t plug just one in the bathroom but start making a mesh network from the beginning and work ur way around the house. Start adding non-battery powered devices first and then add the battery powered devices.