Happiness and purpose are one and the same. The people who are the happiest are the ones who have purpose. They rarely are the ones who feel the most pleasure.
For example, if you ask people with small kids how they feel at any given moment, they usually say they feel like shit. But parents also usually report being happier than almost any other group of people. It's because their lives have purpose.
We all suffer. The ones whose suffering have purpose, are happy. The ones who seek pleasure all the time don't usually have any true purpose, and that's why they are actually very unhappy.