Hi Lelizabeth08 in Scottsdale, AZ,
Well, the thing about "natural" is that large breast implants, relative to one's frame, rarely look "natural." They make look great, hot, sexy, etc...but the larger the implants, the less likely they are to look natural.
There are, of course, no absolutes...but, in general, I would say that those implants on your frame would look a little large. Not that there's anything necessarily wrong with that, and, of course, there are many people walking around out there with exactly that, and even larger.
I generally suggest going with the SMALLEST implant you think you'd want, rather than the largest. And that's with the understanding that no matter what size you choose, you'll probably wish at some point that you had gone larger. That's just seems to be the way it is.
My advice: go a little smaller.
The final decision is, naturally, between you and your plastic surgeon.
I hope that this helps, and good luck,