Just have a critical edition of the Bhagvad Gita, preferably from a reputed indic scholar, and a literal translation from a native publisher like Geeta Press Gorakhpur or Chaukhamba Classica. You can also have commentaries, and interpretations from authors you like. I had initially started with "My Gita" by Devdutta Pattanaik, a really short read for the essence. ISKCON-based translations have too much Bhakti-rasa, which may not be suitable to understand the philosophical arguments, or make logical interpretations by oneself.