I actually was just in a clinical as a student in OB with a mom who was partial breech and the OB did the ECV mom was in labor and had an epidural and the OB manipulated the baby through labor all the sudden baby turned, dropped she dilated to a ten and doc was catching the baby all in 3 minutes. I've seen babies flip during labor when I was a labor and birth assistant, so don't worry yet
It did seem uncomfortable on mom but so did the contractions and timing it between them, also the baby wasn't full breech, but it worked great.
My ds was facing sideways during labor which hurt I spent most of my labor on hands and knees rocking my hips to turn him, and nurse would rub my tummy the way we wanted him to turn, no pain other than labor (no drugs, no inducement) and it worked fine. Let doc give it a try if it hurts too much, it hurts to much don't be afraid to say so.

Both my bios were originally breech, but both turned quite late on in the pregnancy. 35 weeks sounds a little early to perform this procedure - I think a lot of babies are still breech at this stage - if I were you I would ask if it could be left a couple more weeks and see if the baby turns naturally - (especially as I have heard this procedure is quite uncomfortable) - I would think there is a good chance of this happening.

My OB tried on BD#1, but it did 't work. I won't lie, it was not a picnic. The terbutaline made me dizzy and anxious. It did not work and I ended up with a section. While pregnant with BD#2, I declined the ECV because my 2 previous pregnancies had ended in a section and I did not want to incur the risk. BTW, all 3 of my kids were breech and the OBs could not figure out why. Good luck and I hope it works for you!