The only plant I can think of at the moment, is Azalea. I found an article that gives you which type of Azalea to choose. Indoors they should not freeze, I imagine they would drop all their leaves if they did. They are perfect for Bonzi, so you could prune it to any shape you wanted. Although, if this is just not the type of form you want for this room, I understand. If it were my porch, I would experiment with a fern on a tall stand, simply because your porch sounds like the conditions of Victorian homes so long ago that had parlor rooms with ferns thriving in them because the like cooler winters. For me it would be an inexpensive gamble, if it worked It would be great and if not I would keep trying other plants.