I'd like to be able to switch between reading a book on Kindle and listening to it on audiobook. Is that what Whispersync does? I have a basic kindle, 8th generation, 3 years old and, from what I can gather, I can't use this with Whispersync. What kind of Kindle do I need? Is it only some books that can be used with Whispersync? Do I need to pay a monthly subscription to Audible or do I need Audible at all, or something else? Once set up, is it very easy to switch between Kindle and audiobook without losing place? Is there anything else I need know but haven't thought of?