Decide your end goal: tender/juicy (go napa), sturdy leaf (go bok choy), or hearty chew (go green cabbage or kale).
Use the listed ratio. For firmer options, trim to thin ribbons or small pieces so they cook at the same speed as savoy.
Prep for texture: massage kale with a pinch of salt for 30–60 seconds, or thin-slice green cabbage and sauté until just tender.
Cook/assemble according to your recipe. Taste near the end—if it’s bland, add salt; if it’s too firm, cook 1–3 minutes more.
If your substitute releases extra water (often napa), dry-sauté 1–2 minutes before using in fillings.