A simple idea, I used a ceramic bearing 6704 (20x27x4) and printed three parts to it, the outer part for better grip and two inner parts for a good fit on the finger and beauty. The ceramic bearing doesn't need lubrication and glides perfectly, but it also costs more than usual. 

The finger size is limited by the inner diameter of the bearing (OMG), so if 20 mm is suitable for you, then the inner parts are not needed. In my model, the inner diameter is 19.2 mm, so the wall thickness of the inner part is sufficient (0.4 mm), less will probably be fragile. I have attached all the sources, so you can customize as you want.

The outer part is held without glue, so it may take several attempts to match the diameter. And the inner parts were glued together with a couple of drops of glue.

Printing:

Material - ABS (or any other)

Layer Height - 0,1mm (optimal)

Nozzle - 0,4mm (less for quality)

Infill - 100%