Or can someone lend me a cat for a couple of months to sort of try before I buy? Last thing I want to do is to get another rescue cat, have it for a few months and realize Patch will never get on with it, then what do I do? Give up the old one? Give up the new one? It wouldn't be very nice either way...
Patch is still a kitten isn't she? I think you should just go and get another before she grows up and gets more territorial. Borrowing another cat for a while is pointless and mean - for both cats!