Hi Clare,
If you have a look at reviews on you might come up with something close on your list of available hotels.
It looks as if you don't have any other option in light of the fact that you booked the flights separately. Its poor form though that they left it so late to get back to you and surely they should have known this at time of booking. Can your preferred hotel put you on cancellation list? Have you tried ringing the hotel direct and see what they have to say.