Athleta and Title 9 make a note in most of their clothes which ones can accommodate a prosthesis. (sometimes it takes making a slit in the lining and slipping the prosthesis between the lining and the main fabric of the top)
Congratulations on getting out of the drain-game! Are you wearing a bulb, or are you done with drains all together?
The surgical shoulder will roll inwards, the scar tissue contracts like shrink-to-fit Levis. Your trainer will give you mid and lower trapezius and rhomboid strengthening exercises, and pectoral stretches to help counteract the shrinkage. He can also run tight McConnell tape or kinesiotape along the belly of the lower trapezius to facilitate postural correction.
It will all work out in the end. Hang in there!