In my bathroom I have one vanity light and one vent fan (to remove moisture). There is one switch that turns on both the vanity light and the vent fan. I want to add another switch, right next to the existing switch, in a double box to separately control the light and the vent fan. My understanding is that I do not have to run any additional wires. Instead, I just need to get a bigger box and another switch and connect the wires as shown below. Is this correct?