Sorry if you already know or aren't interested. But I've just recently twigged this and love it so much that I want to spread the word!
If you're a member of your local library (which is free - just turn up with ID & proof of address and join), then you get access to its digital services too.
That means a whole digital library of books. I read them on my phone. but you can read them on a tablet/computer/whatever - even on your Kindle. There's an app called 'Libby' which you download on to your device and that gives you access to the library catalogue.
You borrow books, and they get automatically returned on their due date - so no fines. It is absolutely completely free. The reading experience on the app is very similar to Kindle. (If you want to read the book on an actual Kindle, you export it to your kindle rather than using Libby).
The catalogue isn't as huge as I'd like, but I've found lots of things I want to read. I especially like it for guilty-pleasure blockbuster type books that I enjoy reading once but don't want to own. I imagine that the more people that use it, the more money the library will spend on acquiring digital loan rights. (So I have a vested interest in encouraging you to try it out!)