There is an excellent 130-page piano lessons book available tomorrow only for free on Amazon in ebook format. It covers technique and music theory. It isn’t a song book, though. It is meant to replace about 3 years worth of piano lessons. It is made by Steeplechase Arts, and written by a music professor.
If you don’t have a Kindle, you can get a Kindle app for pretty much every smart phone, computer, laptop, or tablet. Once you download it, it will remain in your Amazon cloud so you can look at it from any device that has the Kindle app. The Amazon link will take you straight to the book. There are 30 free videos stored on YouTube to go with the book to get a better handle on technique. The YouTube videos are pretty helpful.
Can’t beat free.