Check out Ryan Holiday's books! There's the Daily Stoic that is a daily meditation on a stoic writing, one page to read and think about each day, and then there's also a journaling prompt one. I use the meditation book, and then often find Ryan Holiday's curation useful, but his trimming of context a bit too aggressive to give him the ability to put it all on one page, so I might read the source along with what is written there.

Most of the stoic writings are letters and aren't super long. They're very approachable!