The best notebook is the one that’s actually with you. Something pocket sized, an A6 or close to it, fits in a bag or a pocket without a second thought, so it’s there when a thought is worth catching.
A plain grid notebook does the job, 32 pages, barely ₹30 a book as of July 2026, with a colored cover version too if plain isn’t your thing. Both are small enough to disappear into a pocket.
A few others came before these. Neorah’s Petite is a longer book, good for writing more per sitting. Accuprints A6 is hardbound, for something sturdier.