5'3", 118 lbs 34A. PS suggests 275cc moderate plus. Good size?

Hello and thank you for your question.   The size, profile, and shape of the
implant is based on your desired breast size/shape, your chest wall
measurements, and soft tissue quality.  This decision should
be based on a detailed discussion with equal input from both you
and your surgeon.  This entire surgery
can be performed with a small incision technique.  Make sure you
specifically look at before and after pictures of real patients who have
had this surgery performed by your surgeon and evaluate their results.  
Best wishes and good luck.
Richard G. Reish, M.D.
Harvard-trained plastic surgeon

Thank you for sharing your question.  Unfortunately without an in-depth verbal and visual description of your goal results, as well as measurement of key breast parameters, it is difficult to offer definite implant recommendations.  Most patients benefit from "trying on" different implant sizers to have the best idea as to what their results will be, while their surgeon supplies appropriate guidance based on your anatomic limitations.  Best wishes