OO, being 1/76 scale, would probably work if you're using true 25mm figures. O gauge, 1/48 in 'Merican, although I personally find it a little large, is much closer. I, myself, would replace some of the smaller doors with ones closer to 1/56, just to scale things a bit closer. But, that's just me.
Cultist #3, I'd check the spelling in your signature if I were you. Iä! Iä! Cthulhu fhtagn! is the correct version. You know what happens if you get a syllable wrong in an incantation! Let's just say that I wouldn't want to clean up afterwards, always assuming there's anything left to clean up!