I highly recommend William Irvine's A Guide to the Good Life, then reading Marcus Aurelius, Seneca, et al. As an aside: I listened to Irvine on audiobook immediately after listening to Sherry Turkle's Alone Together. It was like reading about a disease and then the treatment. Recommend, would do again.
I’d recommend skipping Irvine’s book and just going straight to the sources. I didn’t feel like he added much, and thought his book was poorly structured and overly didactic; too close to the style of the popular self-help book for my taste. I also felt like he projected many of his own opinions/conclusions back on the authors he was discussing.
Maybe my impression is biased by the uninspiring quality of his prose on a sentence-by-sentence and paragraph-by-paragraph level though: I’m pretty sensitive to bland fuzzy writing.