I highly recommend the Bodhicaryavatara by Shantideva! It’s the most significant ethical text of the Mahayana Buddhist tradition, with some serious Madhyamaka metaphysics sprinkled in. I’m currently writing my undergrad thesis on it, and I’d be happy to talk about it.
Here’s a great guide: https://www.shambhala.com/guide-to-the-way-of-the-bodhisattva/. I took an intensive course on the Bodhicaryavatara in the traditional monastic style in Kathmandu, Nepal; see https://ryi.org/programs/degree-programs if you really want to dive deep. The school is currently offering all courses online.
I’m also studying The Ladder of Divine Ascent by St. John Climacus, with the accessible commentary Thirty Steps to Heaven by Vassilios Papavassiliou. St. John is venerated in both the Eastern Orthodox Church and the Roman Catholic Church, but he gets more attention from the Orthodox. I find Orthodoxy fascinating because it has such a mystical relationship-oriented spirituality compared to the legalistic style of both Catholicism and Protestantism. However, this text focuses on individual spirituality; there’s not much discussion of ethics.