I've got the one from Hyzuo. 13 inches in grey suede. I've got both the vertical and horizontal ones. The vertical one fits better. You also have enough space to throw the pen at the bottom of the case if you need to.

At first, I could not close the horizontal one because the magnets were not connecting. After a bit of stretch, it's ok now, but I still prefer the vertical one. You can put the pen on the side in the horizontal one. I still don't have the pen loop to see if I it will stick to the case texture to keep the pen in place inside when I remove the laptop from the sleeve.

Edit: Vertical 13 inches in dark grey suede. They even added the Pixelbook in the supported devices. It wasn't there earlier. Link: https://www.amazon.com/gp/aw/d/B074XP4BGB/ref=mp_s_a_1_1?ie=UTF8&qid=1521821275&sr=8-1-spons&pi=AC_SX236_SY340_FMwebp_QL65&keywords=hyzuo+13&psc=1