Good luck, I hope it goes well.
Have you got the belly belt thing that supports the pelvis? I know mums with SPD get this and tend to find it helpful.
There have been studies on anal and uterine prolapse and EDS III and a vaginal birth can also cause long term pelvic floor problems for hypermobile women - that can not be over come by pelvic floor exercises. Certainly the Rosemary Kleer (the recommended physio by Prof G) said that most of her clients go for section because of risk of tissue damage and significant risk of incontinence in late life
Just in case any first time pregnant mums read this I think it is worth noting that the majority of hypermobile women have had straightforward vaginal births without these side effects, so as not to terrify anybody. Also, most problems with pelvic floor are caused during pregnancy not birth
I hope it all goes well, and you recover well from the surgery, and enjoy your lovely new baby