There are various kinds of clickers, but any should work fine. If you get addicted, you may want to try different ones. The first ones were rectangular and I often got confused about which end to click. Then a few years ago, the i-clicker came out -- I think it was the clickertraining.com people who invented it but am not positive. I much prefer the i-clicker.
I've seen one online that seems to be a finger device, maybe kinda like a finger puppet. That could be handy for those times when an extra hand is needed!