I know by experience that an Aeon Labs z-wave microswitch and a slim Leviton 15A GFCI easily fit into a Carlon single-gang workbox. I have this setup controlling a washlet toilet seat in my master bathroom. The microswitch ensures that the toilet seat and water reservoir is only heated during the hours I am at home. I had to replace the existing (old-style) metal gangbox during this project, but it wasn't that much work.