I think you are looking for the mythical 16-300mm f/1.8 pancake lens that sells for $200. You'll find it in the aisle next to the unicorns.
Seriously, if you want to travel light and simple, you may want to invest in a 2nd camera to complement your 6D setup. A Rebel SL1, EOS M3 or some other brand mirrorless may not offer quite the image quality of your full frame, but it certainly will be lighter to carry.
I picked up a EOS M when Canon was having a its fire sale on their first attempt at mirrorless. The camera, 22mm f/2 pancake, EF-M 18-55mm, charger, extra battery and Speedlight 270 EX all fit in this
small bag. While it cannot replace my 5D3 or 7D, it still can produce high quality images despite it's compromises. But life is full of compromises.