The September cactus

It's producing one confident looking flower. There are other buds but sometimes they come to nothing. This plant was left behind in a flat I moved into years ago. I think it needs re-potting.There's a table in our foyer downstairs full of mostly dead plants.(There is a story here.) I was thinking that maybe a couple of potted geraniums might brighten it up.
(I've just read up about geraniums. I don't think the foyer gets direct sunlight, so this wouldn't work. My living room window would be a better bet.)