New to the ecosystem, speaker question

Hi! I recently joined the sonos ecosystem with a sub mini and beam 2 in a bedroom setting. I love it. I was wondering if it was possible to add some sort of rear speaker to the setup. I'd only want one since it's a smaller room, I just want some sort of rear audio in the mix. What are my options? Can you add a single speaker to my existing set up? If so which ones would work?