Automaton, Scientist
Gothic clothed robot. Not super fetishy aside from the story concept.
Gothic outfit, lots of frills. Even by Automaton standards, their body is unusually stable and they are completely incapable of changing size. They have been researching their own body in an attempt to discover how to make it (and other Automaton, but mostly them) more capable of growth. As such, they needs a lot of samples, and will buy the size right off you.
Their shop buys your sizes off you. Mechanically it's probably not a great deal, but if you're desperate for cash, or about to fire a guild member...
Their questline involves helping their research.