There are so many freely available books in Theravada that the problem is deciding on which I should be reading first
Ha, yeah... and even once you finish some there still so many more to go!...
It's good, isn't it?
What is the final conviction that comes when radical attention is razor-edge sharp? That the object of the mind is mind-made (manomaya). (Ven. Ñāṇananda)
Having understood name-and-form, which is a product of prolificity,
And which is the root of all malady within and without,
He is released from bondage to the root of all maladies,
That Such-like-one is truly known as 'the one who has understood'. (Snp 3.6)