I have been reading through the books of Father Reginald Garrigou-Lagrange. He was a Thomistic philosopher and theologian in the early twentieth century. His book, Reality: A Synthesis of Thomistic provides a single overview of Thomism. There also are companion books for each book in the Summa.
You also could read St. Thomas’ book The Shorter Summa, which is only one book.
Professor Kreeft published a series of audio lectures on Thomism which you can purchase from Audible.
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