DS6 has always adored Carl Barks duck comics (and so have I).
Here are a few good'uns. If you decide to explore these, shop around; you can often get them for $5-10 US.
The
Otto and Uncle Tooth adventure series is very fun, and probably within your son's grasp to read at a sitting; it's hard to tell from across the web, of course.
You might consider some sort of compendium or treasury with short stories that would be about the length of a long chapter in an early chapter book, like these
"scary" stories, many of which are actually quite silly.
The series was never continued past two books, unfortunately, but your son might like the British books "Trouble for Trumpets" and "Trumpets in Grumpetland". They can be quite expensive used, so they're a lurk-and-buy sort of item.
