Oh, is this whole thing operating at 3.3V? If you have enough power to send a HIGH signal to the microcontroller, then you can still use the button by feeding it 3.3V.
What the button does is just make a circuit. When its pressed, it completes the circuit. Since the output is connected to the arduino, and if the whole thing is running at 3.3V and is using 3.3V logic, then getting a t 3.3V from the button will still send the HIGH signal.
What voltage are you going to be using? Is this a 3.3v pro mini or a 5v pro mini.