I used to carry a notebook, supplied by the state, in my hip pocket. About 2.5"x3" or so, brown cover, lined paper, sewn
"hinge" on top, so it took up very little space. Don't know where they came from, but one day they were no longer available, replaced by a spiral top, which does not fit in a hip pocket worth a damn. I somehow managed to come up with a large supply before I retired, so I haven't bothered to look for more. You might try the big box type of stationary stores...
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OBG