protect op amp input from overvoltage from piezo sensor
yes. That's commonly done. Diodes in such usage are called TVS diodes
um, asking for a diode of the right size makes little sense, as you're probably designing a board around this, anyway, if you're looking at SMT? Anyways, yeah, there's plenty of SMD diodes, you'll just have to go to any larger distributor's website (Farnell/element14/Newark, for example) and click through to the discrete diodes and just throw out the packages that are too small for you. You really want to think about simply buying a dedicated TVS diode pair, however.