I'm also often doing creative work off the desk without a mouse or extra keyboard and previously used a MBP 17". But I'm happy I upgraded to the 15" MBP Retina 2 years ago. I use it for everything and have no additional display because I like to put the machine in my bag and work wherever I am.
I recommend to use a 15" for work in Photoshop or Illustrator. A 13" display would be to small for me.
What might be also interesting for you to know before you buy: I didn't upgrade to the MBP with Touch Bar so far. First because the sound of the keys is much too loud (more like on an old typewriter!) and I see no advantages in having a Touch Bar. Second: I often use the F keys for shortcuts in Photoshop and with no tactile feedback I'll have to look down at the Touch Bar to press the right key instead of focusing on my work on the display.
Hope this'll help you.