[F1 Pilot]

Wife's brakes are starting to squeak and pedal feels low. "Check brakes" warning light is not lit. Car has 36K miles. Trying to avoid dealer for brake$$$$.

Has anyone replaced front and rear pads with non-OEM pads?
Do I need to go with semi-metallic or can I replace with ceramic pads?

I was quoted $800 from local mechanic who I trust and has experience working on BMWs. Pads and sensors (if necessary). No rotors.
Thank you!