Hi. Im a complete novice at electrics & need some guidance. Downstairs in my house, I have a double light switch, one to switch the ground floor hallway & the other to switch the upstairs hallway & upstairs. Then I have 1 switch upstairs that controls the upstairs hallway light. I hope I have explained this well... Now the thing is that I want to install a dimmer switch upstairs for the upstairs hallway light. is this be possible?? & which type of dimmer switch do I need, 1 gang, 2 gang... 2 way, 1 way???