Suggestions sound good above.
A couple of years ago I posted some suggestions to this thread. From that post (#220358), for your DS, considering his apparent taste for humor+science, I'd call out:
Phineas L. MacGuire series, Frances O'Roark Dowell -- by Lexile level, it's supposedly about typical 5th grade level, but I don't think it's really that hard -- it may be the occasional scientific vocabulary word pushing the Lexile level up -- incorporates some science into some funny but good-hearted stories.
Dragonbreath series, Ursula Vernon -- this isn't literally "realistic" (as it's about an anthropomorphic dragon and his anthropomorphic other creature friends) and the stories are fantasy type, but it's quite funny in a not-nasty way (my husband kept reading these to our kids for years as he enjoyed them) and it's a hybrid of "normal" text with occasional breakouts into comic panels which may give it extra appeal to a Wimpy Kid fan.
I'd also take a look at:
Time Warp Trio series, Jon Scieszka -- the author is interested in getting kids reading, and in particular interested in getting boys reading. Seems to work well for many boys: get exposed to some history in a fun way.
