Bro’s got a holstered sketchbook. That’s pretty cool. I can imagine you in the Toy Story scene when Woody says “draw!” And the etch a sketch draws a pistol.
If you've heard of lead holders/clutch pencils... I have a suggestion that _might_ fit with the others. The Koh-I-Noor Versatil 5228. It holds 2mm lead, and is a drop clutch mechanism, which takes getting used to. But the thicker lead is useful for shading.
There are definitely smaller ones in length and thickness, but I'm quite sure any of those would fit into the "So small, it's uncomfortable to hold" category. As opposed to the sweet spot you found where it works again after getting a little thinner. Take that with a grain of salt though; there might be a hidden gem in the world of lead holders yet!