Just saw your post. Not much response. I guess caving headlamps and piezo switches are outside everybody’s budget.
I know Narsil or Anduril UI has electronic lockout (4 clicks) among other things. Lexel sells drivers with Narsil. They work with momentary switches (I think piezo switches are momentary but I might be wrong).
If you want to drive one 3V led with 2s you would need a buck driver which are a bit more expensive at 21$.
Or you can use 6V XHP50 and 2S TA Narsil (7135+FET) driver if you don’t mind direct drive (a lot of lumens and heat) at higher modes.
Would you mind sharing photos of the caving headlamp you built? I want to build mine in the future. I use a modded armytek and a modded nicron at the moment.