Bro, just go to aliexpress and get some of those 38W or 55W with chinese tubes, cheap and good. Fashion some reflector with some aluminum foil or something, it shd be possible with how these gadgets are designed. There are some setups that can do 100W-200W in china, not expensive, just bulky.
So is there a reason why you’d need a portable UVC flashlight? I believe the Mateminco 18S is among the most powerful out there already, and the output i believe still does not compare with a 38W chinese tube, though up close it might more more focused. ie higher candela, but small spot, so if you are gonna be treating say a bathroom or heck even just part of it like the bathtub, good luck.
Any plastic safety glasses or normal prescription glasses is sufficient for UV-C and UV-B wavelengths, it will block. I know this from my reptile hobby.
It is UV-A that is more difficult to block comparatively, but still easy to cut that out.
But seriously, with mold and UVC, only the surface would be treated. You cannot use things like bleach or sodium percabonate? Same surface treatment action and much cheaper/faster too.