This question comes up every two or three months, so there are lots of threads in the forum about it.
The short answer is that there are several options for this. See the FAQ which lists all the buttons and remotes that work with smartthings. Each post should say whether the devices for the US or the UK, and whether it is battery powered or main powered, So read carefully to make sure it matches what you are looking for.
The FAQ is intended to only be one or two posts per device, and there’s usually a link to a discussion thread about that specific device. If you have any follow-up questions, either ask in the device specific thread or come back and ask here. Thanks!
FAQ: Full list of buttons and remotes confirmed to work with SmartThings
If you are in the US, the most zwave popular option for this is probably the battery-powered Cooper aspire RF9575 “anyplace” switch. (Eaton is the company, Cooper is the division, and aspire is the model line. It could be listed under any of those three names.)
It comes in two different styles and several different colors. Make sure you match the model number as there is a different Mains powered switch that looks exactly the same. Shop around as prices vary, but here’s an example listing:
You can also get it in a “kit“ with one master switch and one of the battery powered auxiliaries.
Anyway, that’s a very popular option but there are some other choices as well. They are all listed in the FAQ. 