Zwave is also easier. Get an Aeotec Zwave Repeater. It is easy to open and the antenna is immediately visible. With a little tinkering, you can get the mod here too. Please be careful, you are working on a component with 240 volts!
If the power is still not enough, you can switch on a booster in between. But pay attention to the legal regulations in your country.
It is also important to consider the transmitting power of the antenna. The more dbi, the flatter the radio cone becomes.
