In my experience they like a coarse, gritty, fast draining potting compost. Here in the U.S., we call it Cactus Mix, but I'm not sure what the equivalent would be in the UK.

we have cactus mix here too. but where in the uk are you as they don't do winters.
the RHS says 'Strelitzia reginae is not hardy and requires a minimum winter night temperature of 10-12°C (50-54°F...)
so it is really a conservatory plant in the uk unless that's what you were wanting to know for potting it on.

welcome to GoY too :o)