A portable keyboard layout for minimal mental overhead?

Hi all, there are two things I want of an alternative layout:

• reducing mental overhead as much as possible.
• portable, so I can use it away from desk.

The second requirement points me towards layouts closer to 20 keys, like wulphred's wearaboard.

But let's ignore that for a second and just focus on the first requirement: what are the best strategies to removing mental overhead when using a keyboard? And will 20 keys get in the way? (assume I'm okay spending months practicing).

When I say mental overhead, I want to almost forget that I'm using a keyboard. I want to be able to think something, and my fingers start moving to command my computer without me having to put much thought into "how" to do it. Instead, rely on muscle memory as much as possible. My computer already is fully keyboard operable. I use tiling window managers and the terminal plenty.