I see a couple of people have mentioned BookBub & others have mentioned the free Kindle app. I add my vote to both those things.

The Kindle app allows you to adjust the brightness of the screen & its color, the type face, boldness, line spacing, etc. All of that means you can create a very comfortable reading experience.

BookBub will send you an email every day with books at really low bargain prices, usually only available for 24 hours. They are put at those prices for promotional reasons and can include new releases, pre-releases, books from series, etc. An author whose book was included in one of these offers told me that authors get the same royalty for the books sold on promotion as they do for those sold at full price. Nice to know! You can tweak your preferences in order to be (mostly) offered stuff that will appeal to you. These ebooks don't have to be bought from Amazon. Generally, the same deals will be on Barnes & Noble, Kobo, etc.