Wow, I can't believe you went to all that trouble with the weights.
I've thought a lot about how to create a keyboard with zero EMF. Are you so sensitive that you get a reaction even from old style battery powered keyboards that use Infrared light (not bluetooth) ?
I would think those would be quite low EMF. The IR sender is directional, so you can point it to the receiver at a distance.
Transmission mode is infrared, so all light, no RF. 6AA Batteries.
If you still want to go the super-hard route, I'd think something with interrupted light beams, like optical wires, would be the way to go.. So when you press the key, you're changing the light reflected at the end of an optical cable.. which can be quite cheap.
With a photo sensor, optical cables, and a logic board like the Arduino, it should be doable.