The article doesn't mention Moleskine once, yet it seems several comments are about that brand. What's going on there?
Notebooks should be about utility first. I have a Staples brand of 3.5 x 5.5" notepads that come in 3-packs. They are almost exactly passport-sized in terms of height, width and thickness, so they fit perfectly in a pocket, to the point where it's almost invisible. Once I'm done with them, I can store them in an index card box.
THAT for me has been the key to taking paper notes consistently. Create a situation where the friction to start writing on a pad in my pocket is lower than pulling out your phone and getting distracted by a lock screen notification before you can even open the notepad app.