One of my all-time favorite books -- "How to Want What You Have" by Tim Miller, PhD -- has as its central thesis the idea that:
1. Most people are relatively unhappy;
2. The root cause is our tendency always to want More [money/power, love, recognition] -- which stems from evolutionarily adaptive traits;
3. The remedy is to live in the present moment -- which one can learn to do by deliberately practicing three closely-related things:
1. Compassion
2. Attention
3. Gratitude
The book is (sadly, inexplicably) out of print, but it's popular enough there are plenty of used copies for sale. I first encountered HTWWYH in a 5th-edition hardcover, and it was transformative. Highest posaible recommendation.