Have you put up with mainstream, uninspiring, low-tech tree ornaments for too long? This season why not deck the halls with codes of holly?
This DIY Ornament Kit is just the right size (7 cm diameter) for a micro:bit, a 2xAAA battery pack, and however you'd like to dress up your ornament! Your local hobby shop fluff puff balls and other materials will diffuse those on-board LEDs nicely.
Of course you can very easily see the LED grid on your 'bit and the onboard motion and temperature sensors work just fine. For capacitive touch you can use some conductive tape and attach it to the inner surface to create a capacitive touch pad. Since you can't press the buttons easily, try using the accelerometer to detect when the ball is shaken to make it do stuff!