My daughter and I are both prolific readers...she has more spare time to read, but I'm a faster reader! Given the time, we can easily read a dozen books in a week.
A couple of years back I got her a KindleFire and have the same myself. Both are registered to me so we use only my account...which means I ask her to look only for "free" books unless she asks first. I don't like "surprises" popping up on my account...ha!
Anyhow, I found this website months and months ago...and subscribed to be notified about FREE E-books (and books at a great discount) DAILY. I get an email notice every day...here is what one recent one looked like:
When the email opens...it is a list of books. Each has a short synopsis of the book with the current price at Amazon.com
When you click the "Amazon" link...you get the specific book to order.
Always check the "Kindle Price"...the free book should show $0.00 before you click. I have never had an instance when this is not correct...but it is always good to double check before buying.
Here is a link to the website for Bookbub.com so you can check it out yourself...if you like to read! The categories cover a lot of things...we "signed up" for notification of a lot of variety of romance novels, military fiction, and mystery novels.