https://www.amazon.com/dp/B01HR8L2HW/ref=twister_B01GH7X40W?_encoding=UTF8&psc=1
This is what I use. The case works brilliantly. The only flaw I've noticed is actually a design of the Apple Pencil's software itself. When in the case and the iPad is being used, the Pencil is motion, so it drains battery. The Apple Pencil was apparently never designed to always be attached to the iPad (hence probably why Apple doesn't offer a good solution).
I still get a day or two of relatively heavy usage out of the pencil (I'm a musician and I use it for annotating music all the time) but I used to get more time out of it when I didn't have it constantly attached and in motion.
There are also several versions on Amazon that work with the Smart Keyboard (they just offer the back cover/Pencil holder, not the flip/fold front).