I use one plugged into a thunderbolt 3 dock so I can have a great desktop setup with a single wire, and quickly unplug when I need to move.
It's a shame lenovo stopped updating the 12 inch X series as it would be the obvious answer to this question.
X280 - 12.11 x 8.26 x 0.7 in
X13 - 12.2 x 8.6 x 0.7 in
The X13 is the old X 12in size.
I would still take the Carbon probably. One thing I like about it that is underrated in reviews is its flexibility. People think they want a rigid, aluminum milled laptop, but I actually quite appreciate how the entire computer can bend slightly, as an alternative way to make it more durable.