There is a 100% chance of rippling.
"My doctor told me that due to my extreme thinness and thin skin, rippling on the sides will definitely occur" - He is honest and truthful.
ALL breast implants produce ripples - but some produce less ripples than others AND in some people such ripples are less visible and palpable than others.
In general, saline filled implants ripple more than do silicone gel implants (Just fill a ziplock bag - hold it by the bottom and see for yourself). The more cohesive gel implants produce less implants BUT the more cohesive they are the differ they are as well and begin to fill very unnatural.
The question you should be asking is : "How much coverage can my current breast diameter provide to cover up an implant sitting underneath it to cover and soften such potential rippling?"
1. That is the MAJOR reason why implants are placed under the muscle
2, the wider / larger your breast tissue, the wider the implant that would look natural under such breast without the tell tale rippling of an implant that is too large especially when leaning forward without bra support.
So - I would recommend gel implant placed UNDER the muscle and sized by your current breast coverage. That is sure to minimize the extent of visible and palpable rippling.
It sounds like you are dealing with an honest Plastic surgeon who is not trying to "sell you". You may want to listen to him even if you do not like the answer. You will come out ahead in the long term