Here is an answer to @ElsieD' s problem of Napa cabbage being too much for her needs (If she can find them). Many needs I would think.
Also available are 娃娃菜 (Mand: wá wá cài; Cant: waa1 waa1 coi3) which is 'baby cabbage', a small growing version of Napa. Particularly popular in Sichuan, but available widely. Perhaps bizarrely, these are sold in supermarkets in packs of three, rather defeating the point. However, I am able to buy them separately in wet/farmer's markets.
I didn't measure them, but they are about ⅓ of the size of Napa. I'm glad they are clean!