These Micro Flat Button Coin Vibration Motors are perfect to give your project that tactile response you need. They work great on wearables or the back of hard surfaces.
They operate on 3V, and come in 10mm, and 12mm in diameter.
Note: be careful with the wiring, or reinforce the solder joints on the motor with hot glue. The joints and wires are delicate and will snap if left unprotected.