I asked the surgeon about this prior to my CS as I too was coming down with something. Basically you would have to be terribly unwell with a bacterial infection before they would think about postponing. I too was worried about coughing - however I have since found out that codeine is an effective cough suppressant so if you are coughing afterwards ask about adding codeine to your pain relief options. As it turns out I was worried for nothing and actually felt quite well on the day.

Good luck, enjoy meeting your new little one - every blessing for your birthing time.