I find introductory textbooks created for those who study the subject at college / university a nice middle ground. They are not always cheap or in ebook form

I find introductory textbooks created for those who study the subject at college / university a nice middle ground. They are not always cheap or in ebook form so libraries are useful. They require more effort to read than popsci books but you learn so much more and they are considerably easier to digest than academic papers.