Looking for the best overall study of Samkhya. Reading Patanjali and that’s already very enriching for the context of EB, but an in depth treatment of Samkhya would really help.
The Samkhyakarika is the classical text. There are a number of translations with introductory comments, etc. online. But here’s one.
Secondary sources … Classical Samkhya and Yoga … don’t hold me to it. I can’t tell you if it’s worth over $50 and I get my hands slapped for reading Routledge books, but they can be simple and clear.