This is a small but mighty collection of battle-tested, fully-custom brushes for Autodesk Sketchbook (Win/Mac desktop version*).
Rather than creating a big collection with a lot of filler, I'm only including brushes that I use frequently, and that fit into gaps in the default brush library. These are brushes I love to use in my own work, and I've been fine-tuning some of them for over six years.
All of the paper textures tile seamlessly and are at least 512 x 512 in size. They hold up well at 4k and beyond while still being responsive to use on my six-year-old Thinkpad Yoga. If they feel sluggish to you, the easiest way to improve performance is to slightly increase the "spacing" and "flow" values in the brush's settings.
* I have no idea whether the iPad/Android versions of Sketchbook allow for the importing of these kinds of brushes. They are intended for use on the Windows and Mac platform. However, if you try them on an iPad and they work correctly, please let me know!