After much back and forth with Cartier sizing, and the purchase of 2 cuffs, my rule for cuff sizing is to go up 2 sizes from your actual wrist measurement. I have a 16cm wrist and my cuffs are size 18cm. They fit comfortably in all seasons. I sleep in them comfortably with no pinching or marks.
Beautiful stack! What you have said has been exactly my experience with wrists the same size as yours - I also wear size 18 in the cuff and it fits perfectly
