I work in theatres and have seen a good few bariatric procedures, the patients remain in their gown throughout procedure however we do lift gown to around about under the breasts, I've noticed a few patients have opted to wear one of those crop style bra/vests, these are ideal as they don't have any metal in them and can be easily manoeuvred up out of the way if needed and there is also no problem with wearing own pants which means all the embarrassing parts are kept covered, once the abdomen is exposed the rest of the body is completely covered with sterile drapes so nothing at all is exposed during procedure, hope this helps put your mind at ease