I agree that letting him choose things he wants to read is definitely the surest way to progress in reading.
We move from first grade readers to the Pathway readers, then into the easy to read chapter books. My first grader loves reading for himself what we are studying in history, so we get books like, “Sam the Minuteman” and “George the Drummer Boy”. We have really enjoyed the “I Can Read 3” series, as a whole.
Once my kids can read fairly fluently, we move into easy chapter books. Honestly, I have found the Sonlight list of readers to be very helpful in the beginning stages. I don’t like their curriculum as a whole (for us) and I don’t agree with some of the books they use in grades 3 and up, but for beginning readers I think their book list is fairly helpful.
Be sure you let him progress at his own pace!