My BS Gongora galeata is pretty compact, not sure if it'll stay that way or if I'm just not growing it well, but it's been around the same size for years.
Sievekingia, Xylobium, and particularly Schlimmia all have species that will stay small, going by the few I've seen of each. Most Schlimmias are from higher altitudes and need cool conditions, but I think there are one or two warm growing species.
I recommend checking with Gary Meyer at
Colombian Orchid Imports. His sources seem to carry a lot of harder-to-find Stanhopeinae, and the one time I ordered from him the quality and communication were very good.