Installing a light fixture in a storage closet

wvphysics

I have a closet under the stairs, one of the 180 degree stairs so the closet curves around for plenty of storage. I want to put in a light and a switch. The basement is mostly unfinished, howver the closet side of the wall and the ceiling is finished. the ceiling also is completely sloped and comes up to only about an inch above the door frame. My best solution is to get a small light fixture and place it on the wall because it doesnt look like there would be much room in the ceiling, nor is there easy access to run wiring even from the unfinished side of the wall. The question i have are, what is the appropriate way to install a surface mountable fixture on the wall, is there an old work box that is approved to support this, or do I need to use new work box and install it from the unfinished side? Also, in the NEC code, all I can find about clearances for wall mounted lights is recessed and lights over the door, my situation is neither, so what sort of clearance would I need?