I think given the options you are looking at, sweeping of the membranes is pretty benign. Although many here are against cervical checks, I am not. I like them as a patient so i know what is going on, and I find them helpful as a midwife. As long as the ob follow proper handwashing/gloving techniques, I wouldn't be too worried about it. The actual infection rate is very, very low.It can be painful, usually not too bad.
That being said, sweeping may do absolutely nothing for you. And I totally understand about sex. Just the thought sounds painful to me (and that was before the broken rib). And the contractions and cramping after sex that I get are worse than sweeping. Are you doing anything else? Like evening primose oil?
Good luck, let us know how it goes?