Made me laugh! Swear I keep the notebook, fountain pen, pencil, ballpoint/gel pen economy going on my own.
I have the Traveler (large) Midori, Passport size and then Field Notes notebooks with or without a Field Note sized leather cover. Love them all. Everything is a trade off.
Traveler is nicest to write in. Great paper choices. Has the option if needed to turn 90 degrees and write wider across. Suppose you could do the same and write across the fold but that bothers me. Most always I just write on the narrow pages, but the other is an option. Carrying is harder for me as I no longer carry a purse and though I have, never got into carrying a backpack, messenger bag. If I used a backpack/bag would probably lean to Traveler.
Passport size is better to carry but the wider width limits the pockets I can slip in. Still nice paper and options.
Today my choice is Field Notes (3.5x5.5). Fits in any pocket, jeans, jacket, hands free. At home will use a nice ballpoint or Uniball for writing. When going out will take a vintage Bullet Pencil with a nice writing nub. The bullet pencil fits in any pocket and doesn't stab me. So many wooden pencils now are beautiful writers, smooth and dark. For me as much pleasure as a nice fountain pen.
I choose carry-ability over FP friendly or page size. You will choose differently and your choice may change over time or for a situation.
-- Another small carry to ponder is something called a "pocket briefcase". Levenger online sells versions but you can find other brands less expensive. -A leather holder for a few 3x5 cards, usually with a slot to hold a few more. Fits in any pocket, good for quick notes. They also sell a Slim Wallet Writer. It holds a few blank business cards for note taking. You don't have to buy these items but can often repurpose something you have. Being creative flexes your brain.
Lots of fun things to do with information gathering.
Thank you for giving your insight on how you use your Midori. I always love reading how people use them and the best way to integrate analog and digital together. Can I assume you are using the Passport sized Midori?