( I’ve moved this to projects so you can get individualized responses based on your set up.)
First things first: you cannot use a regular lighting control dimmer to control a fan. The physics are different.
If the fan and the lights are on the same load line, then all you can do is on/off of the lights.
If you’re willing to separate them, then you can have the lights dim and the fan as an on/off, so then it becomes a question of what physical devices do you want at the switch and is it a single gang or a double gang.
The easiest thing to do for your current set up would be to use a two button single gang switch with one button that does on/off for both the fan and the vanity lights and the other button that does on/off for the other light. Pretty much the same thing you have now.
Anything else is going to require some rewiring.