Diana Winston does an excellent job connecting the path of deliberate mindfulness typically practiced in Insight Meditation and the practice of natural awareness. Her book The Little Book of Being: Practices and Guidance for Uncovering Your Natural Awareness is an excellent introduction to classical mindfulness and natural awareness, and is highly recommended. You can find an introduction to her teachings on natural awareness here: 3 Ways to Uncover Your Natural Awareness
Loch Kelly also teaches effortless mindfulness, the term he uses for natural awareness practice. He has a background in classical mindfulness but was mostly influenced by Tibetan meditation practices. Kelly’s teachings provide a modern secular approach to the practice of effortless mindfulness, his adaptation of those meditation practices. His book The Way of Effortless Mindfulness: A Revolutionary Guide for Living an Awakened Life provides a very good introduction to this practice. You can visit his website to find out more about the books and the app he developed, Mindful Glimpses: Loch Kelly