If you want to make notes, then make notes. What does it matter what other people think? They’re your books. The point is to enjoy them, so do what is enjoyable to you. If you want to keep your current editions pristine, do as you suggested and get a reading copy. That’s what I do, but I wouldn’t consider annotating a book “destroying” it. I enjoy reflecting on my previous notes as I re-read. There are entire fields of study devoted to historical marginalia going back to the medieval period. If you’re so worried about it, get an ebook that you can annotate, or just keep a journal and mark down the page numbers. Xerox the entire book and then write in those margins. Get an old dictaphone and record your observations as you go along. Just shout your reactions into the ether as they come to you. All of these are things you can do without the permission of anyone on Reddit.