I have a room with about the same width. In determining screen size, you might want to take into consideration of the projector, throw distance, is it completely light controlled, screen gain, and seating distance.
I chose to go with a 110" so that I could get the amount of brightness with a near unity gain screen in low lamp mode while dialing down the iris. The room is completely light controlled and I didn't want to worry about shimmering from a higher gain screen. 120" pushed the limits of my projector (with the closed iris) where increased screen gain was most likely required.
My seating is slightly closer making the viewing angle larger than some specifications, but it is very comfortable and encompassing.
By the time I added in the center, front, and subs there was not much room left. I felt lucky to have gotten the 110" due to the center and sub taking up more space that I had imagined. I didn't want to stack the speakers right next to each other nor did I want the speakers right against the wall.
I found it's all about compromises. Getting the projector and playing around with screen size is a great idea.
Good luck