Here are 2 blu-tooth keyboards that I have used with much success. They allow you to use the following devices
appleTV 3rd and 4th gen
This first one is the Logitech easy switch k811. This one is the same size as the apple bt keyboard. Difference is, it can connect to 3 devices. The way to do this is select a function key 1 threw 3, and pair your device. After it’s paired, hit f1,2, or 3, to select the device you want to control. Find it here.
The 2nd one is a bit smaller, and only controls 1 device. It’s only 10 bucks, and is very durable! I have dropped this keyboard down stairs, on concrete, and my kids have even stepped on it, and it still works. I wouldn’t test those theorys Though. Find it here.