Of course it's fine to want for your own happiness. Even solely for your own happiness. But how would you recognize happiness without sadness, pleasure without pain? I'd like to live forever too, but to be constantly happy with a big smile on my face?
https://www.youtube.com/watch?v=CZplzRg6ZP4
https://www.youtube.com/watch?v=CZplzRg6ZP4