You might want to try The Expanse series of books. They're very straight forward but still are engaging with interesting ideas and they've certainly got volume. The language is simple, in a practical and modern kind of way, without feeling dumbed down. It doesn't use any of the structures that can make a book challenging to follow.

I second The Expanse series as the other poster said, I started reading with these books when I had time to read during travel. I love the story and characters and the bookies have a really nice cadence to them with regular chapters breaking up the story, helping you feel the progress.

Another series I recommend is the Silo trilogy, Wool, Shift, & Dust. They've also just started a TV series on the first book