well, 'happiness means' = this is the real (dictionary) meaning, so that's unnatural.. however, you said 'to me', so it's ok.. However, a more natural way to say it is 'For me, happiness IS.. Also, 'having something to do' is strange because it's not special.. everyone has things to do! So, the best way is: "For me, 'happiness' is having someone to love and doing something you love to do"

In my opinion happiness means.....

Yes, that makes perfect sense!

Your statement is grammatically correct and makes perfect sense. Cheers!!