I can’t give much advice on hard books, but I’m writing a book myself and I mostly read it like I read any other books. Kobo has a phone ebook app that you can use, though it’s kind of trash sometimes. I prefer using the Kindle app for stability, but for both it’s easy to take notes in-app. Since it’s on my phone I can either spend a ton of time with it, or if I just want to read a bit while waiting for the bus or metro, I can do that, too. I can just transfer the notes elsewhere when I have time.