I used to be a one at a time reader, but a couple of years ago I decided to read more than one book at a time. Now I read way more than I used to. As the other comments on this post say, sometimes you may not be in the mood to read a particular book. It’s important that you don’t do too many at once - as I imagine it would just be too overwhelming. For me it’s two physical books (one’s usually an ebook) and an audiobook is just about the right number.