As long as you are using the smartthings hub, any device which can talk to the hub can be used to trigger an on/off event for any other device which can talk to the hub. The switch sends the request to the hub, and the hub sends it over to the other device. 
There are many options for these. See the following two threads. The first is a recent one with someone who had basically the same use case you are describing. The second is an FAQ that lists the button devices that work with SmartThings. Many of these are battery operated, so can be placed anywhere. And some are Wall mount, some are handheld, and some can be either. Just read the descriptions carefully to find ones that match what you are looking for.
Also each post in the FAQ typically has a link to a thread that discusses that device, so ask any follow-up questions in the specific device thread, not the FAQ itself.