Patrick is right, some cat breeds that are perfect for apartment life. We've actually wrote an article a few days ago about 8 cat breeds who are perfectly happy living in a flat. Cats a wonderful creatures, they can easily adapt to any environment as long as they are feed, watered, taken care of and have plenty of toys to play with. Make sure though, if you get a cat in your flat tocat-proof your apartment (balcony/windows).
Hello Jo,
Personally, I think cats are happier in a house where they can explore, but as long as they have toys, scratching posts and other things to keep them busy, I don't see why they can't be happy in a flat. My cat Jewel lives with me in a flat and he's absolutely fine :)
Good luck with your research!