Athenaze. Introduzione al greco antico. Con espansione online. Per il Liceo classico: 1

If you're looking at the English versions there are Vol 1 & II. Each of those has a textbook and a workbook. You'll want to start with Vol 1 textbook. This one. https://www.amazon.com/Athenaze-Book-Introduction-Ancient-Greek/dp/0190607661 You don't need the workbook. There's also an Italian edition (https://www.amazon.com/Athenaze-Introduzione-antico-espansione-classico/dp/8895611497 ). Some people like it because it has additional supplementary readings. But all the instruction is in Italian so you'll probably find that challenging if you're an English speaker... I wouldn't recommend it for a beginner. Athenaze by itself is probably not enough comprehensible input to get very far w/o a teacher / addl instruction. If you look on the resources page in the sidebar there are additional books that are recommended parallel readings. But the one I linked above is a good starting point.