That sounds very difficult. I've never heard of someone having their sternum removed, just reshaped (in the case of pectus excavatum). There must be something in there to hold the ribs together in the front, right?
I'm no help here but I do hope the infection settles down and you feel better. As for some kind of brace or support, I can't think of anything since the ribs have to flex as you breathe. Perhaps someone else has heard of this kind of situation.
I had a sternumectomy in '08. There is a space between my rib cage of about three inches, that is contantly invaded by a thorax that coughs. The sternum was removed and also 7 costal cartilage connectors, between ribs and sternum. My chest moves constantly and has for 7 years. Pain graduates to soreness, like having a cracked rib all the time. But then you adjust, and life goes on.