I haven't been around a lot of newer GM HD work trucks, but I've had several Ford and Ram XL/Tradesman level trucks in the last few years and they both offer what you're looking for. Low end trim with just the right creature comforts. They also have ones with roll yer own Windows too! Unbelievably.......Personally I'd pay extra for rubber floors over carpet but I'm a little ocd and rubber floors are easier to keep clean, lol.
For your use I'd go shortbed. Even if you're thinking about a 5ver. It's not going to make much difference towing, but it will the other 300+days a year you're parallel parking it and plowing snow.
I also wouldn't think twice about a newDmax. Arguably the most solid choice of the big 3. (Let the fight start!haha). And if you wait for the '17 models they got class leading @ss whoopin power again! 445/910 baby!
I'll throw my plug in for the Mega Cab with a back seat full of kids though. Course you've already been up sold from a used gasser to a new diesel already!
Being able to recline the back seats part way allows them to sleep upright if you're a seat belt stickler and the extra room and storage behind the seat, even reclined, is nice.
What's another 3 grand? Haha. Wish they made a tradesman mega cab though. Would put a base model mega 2500/3500 diesel 4x4 right in the $43k range at the discount dealers.