I going into a workplace where I should be dressing shirt and tie etc but I always have the same problem with shirts. Non fitted shirts fall like a tent all over. Fitted shirts i'm bursting out at the neck with horizontal stretch lines tight across the shoulder line front and back... the chest is usually alrightish in that it doesn't crease up but if i up the neck size the already tent like shirt below the chest becomes as ridiculous as a non fitted shirt.
I seem to be left with the option to either look like i'm wearing a sail or trying out a lycra suit whilst being strangled
My brother was the same way had to get them altered or custom made. The later was pricey.
I have pretty much the same problem, sans the neck. I don't even have a large chest, but swimming is a bitch and has blessed me with man shoulders that force me to size up for most shirts, making them fit the rest of my torso like you said, like a tent. I would tell you to stick to sleeveless dresses w/ jackets for the workplace, but that would be a bit inappropriate
I've had that problem with girl's shirts but all I have to do is get a guys shirt. And that works for me. But not sure how/what might fix your problem. How long would you have to be dressed up for?