One website for all happiness source is https://positivepsychology.com/. I have mentioned some of the benefits earlier but this article describes the proven and well-studied benefits of happiness.
1. Healthy heart: studies have linked happiness with improved heart health and lower risk of heart disease by 13-26%.
2. Ability to control stress better
3. Better immune system.
4. Overall Healthier Lifestyle: Better diet and physical activity and sleep.
5. Better control of pain.
6. Increased life longevity.
7. Improved work performance