I got it.
LuxPro LP601V3.
https://www.amazon.com/Lumen-Tactical-Handheld-Outdoor-Flashlight/dp/B07KCYQ2MY/
Takes 4×AAA in a holder but perfectly fits a 21700 (or 18650 even without a sleeve).
It’s got a rubber sleeve on the battery tube for a good grip.
It’s got an easy-actuating tailswitch which might as well be an e-switch it’s so easy to click.
It’s multimode, but has no memory, so will always start on high (~450lm) after a few seconds.
Click on, click off, no click’n’hold or half-clicks or anything.
Nasty XP-G3 piss-yellow corona, but a swatch of DC-Fix (bug Boaz for some) will clean it up and make it beautifully floody. Think it’s the #7 film I used on all my LuxPros for exactly that reason (to cure the G3 curse).
15bux, well worth it. Mum will write you back into the will if you get her this light.