This handle was created in Tinkercad.  It has a port for the button and one for the switch, and it matches the exterior dimension of the fiber optic bundle while leaving the right amount of space inside for the Neopixel Jewel and the electronics.

I added a ring around the base to keep it from slipping out of my hand, and a hole in the ring to attach a wrist strap for extra safety.   Add your own details -- every Jedi's lightsaber handle should be unique.

It prints with no supports needed.  The largest dimension is the height -- it is 119mm high, which was just under the size limit of my Up! Mini 3d printer.

I found it printed best using the "fast draft" print setting.  The higher quality settings overloaded the printer, possibly because this model is so close to the size limit for the bed.  Your results may vary.

If you don't have access to a 3d printer, you can order a pre-printed handle from Shapeways.