As you note, I typically use Kindle and save my highlights. Back in the days when I would read physical books, I always wondered about something like this product, but I never tried it: https://www.amazon.com/Scanmarker-Air-Digital-Highlighter-Translator/dp/B01N07J2AE/ref=sr_1_1?ie=UTF8&qid=1487543445&sr=8-1&keywords=digital+highlighter