Using a ready-made touchscreen won’t work behind the glass (you don’t really wanna use foil for this).
either you go for a capacitive touch foil mounted on the inside of the glass or an IR-frame mounted on the outside around the glass.
The IR frame is the cheapest way to for touch functionality, the touch foil slightly more expensive, especially if you go for a bigger sized screen (30"+).
the voice control is probably the easiest and cheapest controller for a mirror to implement thanks to all the voice modules!