I don't know about narrow shoulders, but I am slim and I absolutely would not be without my hug-a-bub. I used to think it was hard to put on, but now i'm a dab hand, and can do it quite quickly. I have a Baby Bjorn for super quick trips (in and out to daycare) and a hip carry/ring sling for around home etc. But for extended carrying and walking and sleeping etc, i personally love my hug-a-bub.
Oh, and DH is about 30kgs heavier and it's uber-comfy for him too. It just wraps around him one less time!

If you live close, I'd be happy to let you try it out.