I'm 39 weeks with DC2, and have requested no pethidine or diamorphine on my birth plan - if I need more than gas and air, I want to go straight to epidural. If I am too far gone (ie more than 8cm) at that stage, I want to stick it out, if at all possible. We'll see 
I really really struggled to BF DD. Everyone said her position was right, she was latched on etc etc, but she was so drowsy those first few days, she just had no inclination to feed. I really feel that was down to the 2 shots of diamorphine (they don't use pethidine at my hospital) I had during labour. My labour was so long, I went on to have an epidural too!
At the time, the diamorph was heaven, as was the epidural when I had it, but hindsight is a wonderful thing.....
Obviously, I do not have a shred of evidence that the diamorphine caused the feeding problems. I may have exactly the same problems with DS, and have gone through a (possibly) more painful labour than necesary. But for me, at least I will know I have done my best to BF. Don't get me wrong, DD is a very happy, healthy, energetic 2.5 year old, and I really don't think formula has harmed her in any way. And I probably would have given up BFing after 4-6 months anyway. But at least it would have been my choice.
Sorry for the long post, as you can tell, it had a big effect on me and I feel strongly about it this time round.
Good luck with whatever choice you make :)