It’s probably simpler than you imagine. 
Z wave is a mesh network: by design pretty much any mains powered Z wave device will repeat messages for other devices. Battery operated devices generally do not repeat. This happens automatically, you don’t have to do anything.
I suggest you read the following FAQ (this is a clickable link) and it will explain the basics:
Then read the FAQ on wireless range and repeaters, which covers both Z wave and Zigbee. Start with post 11 in that thread, then go up to the top and read the whole thing.
Between those two, you will have pretty much all the information you need to begin planning. Just remember that zwave repeats only for Z wave and zigbee repeats only for zigbee.
As far as specific devices to act as zwave repeaters, you definitely do not need the single purpose stand-alone devices that do nothing but repeat. To be honest, they are just a waste of power. And an outlet. The dual purpose light switches, plug in pocket sockets, inwall relays, and plug in zwave sensors do everything that the single purpose devices do plus something else, so they are generally a much better value.
Specific Devices
When it comes to selecting specific devices, people who are going to use Z wave light switches or Z wave inwall relays usually find that those are all the zwave repeaters they need as long as they have enough of them. Z wave plus will have significantly longer range than the older generations.
People who are using Lutron or zigbee or WiFi wall switches but still have other zwave devices that need repeaters to reach them, like valve controls or garage door controls or battery operated zwave sensors, often use plug in pocket sockets.
Lowes makes a pocket socket for their Iris line which is very unusual in that it is a zigbee on/off Device but also contains a Z wave repeater. That lets you repeat both protocols from a single device, which can be very convenient. You can buy this device from either Amazon or Lowe’s, but it is often on sale in store, so I think most people buy it there. (Note that it must be model 3210, there are other Lowes iris smart plug models which do not work with SmartThings or which do not have a Z wave repeater.)
https://www.amazon.com/dp/B01GCKAED4/
But there are lots of other Z wave – only pocket sockets which also work very well if you have a preference for a particular feature or look instead.
So read the two FAQs and then you should be ready to start looking at devices. But you don’t have to look for anything special: pretty much any Z wave certified mains powered device will act as a repeater.
One more option
BTW, this is also mentioned in the FAQs, but as it happens, zwave lightbulbs also work well as Z wave repeaters. That’s not always true for zigbee, but it is true for Z wave. This can be useful when you were trying to get signal through an area where there are a lot of architectural barriers, because the light bulb is High up and can often go in places where there are no outlets.
https://www.amazon.com/GoControl-Z-Wave-Dimmable-Light-LB60Z-1/dp/B00PJH16UC
Although the bulbs themselves are quite inexpensive, typically around $15, if you also want a wall switch that works with them then you are adding the cost of that second device. ( The bulbs themselves have to always be on power, or they cannot function as repeaters. So you can’t just use your regular switch with them if anyone might turn them off at the switch.)
So a pocket socket on sale may actually end up being less expensive, but the bulbs do let you position a repeater high up in a room, which sometimes helps.
That can be particularly useful in a garage where signal gets blocked by the cars or to bounce signal down basement stairs when there are pipes or other barriers running along the basement ceiling.
We had one community member who was working on a large church building and bulbs turned out to be the best way to get signal across a very large room and down a hallway which didn’t have any outlets. So just one more thing to keep in mind. 