You’re spot on - I tried the above set up in a blank project and it works a treat.
Digging a bit deeper I’ve found what the issue is: the camera boom is attached to a socket on the third person mesh. The camera position dictates the First or third person state. So of course when I get rid of the mesh, the camera boom isn’t attached to anything and brings the system crashing down. I’ve been pulling the rug out from underneath myself. At least I know now. Back to the drawing board.
Cheers for the help 