Oh, for heaven's sake. It's restricted by ship type rather than ship size? Gee, thanks, Frontier.I suppose you know by now, but I'll add to the thread in order to save anyone else a wild goose chase. Only the Orca and Beluga can carry luxury cabins. I just wasted three hours of my life flying around in my Asp not finding them on any of the stations listed by EDDB. After six months away I had forgotten how uninformative this game is.
But, seriously, thanks to Rimsplitter for shedding light on it.