The only good notebook is the one you’re carrying. It’s no use to you if it’s still sitting at home because you don’t want to bend it or it’s too difficult to carry or you can think of any other excuse to not have it with you at all time. The only good notebook is the one you can afford. I wrote the first draft of an entire short book in a reporter-style notebook I bought in the local post office for 50p, and that was only a few years ago. Stephen King doesn’t write ideas down because he believes that if he doesn’t remember the idea later, then it wasn’t interesting enough to be in a book. You are not Stephen King.
I, and other writers I know, fetishise notebooks because we work in them a lot and we eventually get picky about them and have disposable income for that sort of thing. We don’t get out much. But I started out writing in the cheapest notebooks I could find. My earliest professional comics work was all roughed out in crappy notebooks on the back table of a late-night burger bar with a Biro, scribbling away at three in the morning while drunks and ravers with nerve damage staggered in and out of the place.
It doesn’t have to be an expensive or fancy notebook. It just has to be the one that doesn’t leave your side. Write it down.