I would use
Morton. Easily. It's not on my list or anything, but it's adorably dorky and I like it. Pluse
Morty is sweet, I think. But it wouldn't need a nickname.
Morton is great!
Norbert is too old-man-y for me.
Three boys nappin', one mama namenerdin'
To peruse my top 100ish names:
http://www.behindthename.com/pnl/82589
He is becoming greater, I am becoming less
Bits of the journey here:
http://jodifriesen.blogspot.ca/And some family cuteness here:
https://www.flickr.com/photos/41705228@N08/