A Repeater will be a good idea. It’s helpful to note that pretty much any mains powered Z wave devices will act as a repeater, including a plug in socket, A plug-in motion sensor, a light switch, etc.
There’s no reason to buy a single purpose repeater – – they don’t do anything more than the other devices do. They were helpful back during the third generation of Z wave when not all devices transmitted at maximum power, but these days you might as well just get a dual purpose device and get more for your money that way.
http://thingsthataresmart.wiki/index.php?title=Repeaters
Once you put the repeater where you want it to be, just run the zwave repair utility and any other devices will begin using it in a day or so. It can take a little while for all of the address tables to update, so be patient.
You might also find the following FAQ of interest. First read post 11 in that thread, then go back up to the top and read the whole thing. ( this is clickable link)