Mapbox has a document for using a gaming mouse to increase mapping. I build a custom keyboard and assigned JOSM’s shortcut keys, because unfortunately, I couldn’t find easy to use multi-featured trackball.

I built a keyboard is custom keyboard kit called “Dozen0” with 12 keys.

The shortcuts assigned to the 12 keys are follow image.

Key assign are optimized for buildings trace because many of my mappings are buildings trace. Can expect an increase in mapping by operating the trackball with my right hand and using Dozen0 with my left hand.

Even with a normal keyboard, it’s possible to improve mapping, handling the shortcut keys with a hand that is not using a mouse, but it will be more easier to mapping by narrowing the keyboard.

Some custom keyboards allow you to change the key assigns, some require assembly from electronic components. Look for a gaming mouse or custom keyboard you can also get it ;-)