Internal Alchemy for Everyone by Chungtao Ho is a good one. Title is kinda funny leading some to think it's going to be a quick-and-easy version when in reality it's the opposite. The practice is described in terms anyone can understand, but it pulls no punches in laying out a path that takes extraordinary level of devotion to reach the later stages. Theory is cited directly from Cantong Qi, Wuzhen Pian, Xingming Guizhi, etc.