It will be a little hard for him to switch from twaddle but there are some great books.
Has he read any of the Narnia series? Boy of the Pyramids was a great book my kids enjoyed in the SCM Ancient Egypt history module. Swiss Family Robinson might be too hard, but my son has read that over 15 times:) It has a lot of adventure in it.
If you have a Kindle, or the Kindle app on your computer/ipad, etc. look up books by Edith Nesbit. My son really liked Book of Dragons/Book of Beasts/Five Children and It, and many more of her books. Gone Away Lake was a book both my daughters and son enjoyed.
If you go to the bookfinder here on SCM and put leisure in the search box and select the grade you want, lots of book choices will come up. That’s been very helpful for me.
I think it’s okay to mention other curriculums on here, but I also like to look up book lists for my child’s level on Sonlight.com, or My Father’s World and They have great books listed we use for literature/free reading. There are also older posts on here with great book lists for boys. You could look up 9 yr old, or books for boys in the google search box on the bottom right of the forum, and you will get lots of great suggestions you can save as a favorite to refer to later.