<em>The Pursuit of Happiness - God's Way: Living the Beatitudes</em> by Servais Pinckaers, O.P. I cannot recommend this book enough. It's solidly rooted in Scripture and St Thomas but at the same time very accessible and quite short.
Small book. Pricey because it's out of print, but great nonetheless. https://www.amazon.com/Pursuit-HappinessGods-Way-Living-Beatitudes/dp/161097493X