The Sientra smooth round moderate high family of implants, despite the name, actually has a high profile shape that is somewhere between the shape of a Mentor high profile and an Allergan style 20. It would give a lot of upper pole fullness - perhaps more than you want, although that is a matter of personal taste.
You didn't specify which Natrelle implant the other surgeon recommended - there are several families. Based on your description, I would suggest instead either the Sientra smooth moderates, Mentor Moderate Plus or Allergan style 15's. This is the type of decision that needs to be sorted out in person, though.

Thomas Fiala