Hi there, congratulations on your pregnancy! I'm currently 34 weeks pregnant with Baby no.2 and have been agonising since week 20 about whether to birth this baby naturally or go for an ELCS. I don't want to hijack your thread and go into the looooong details of my particular case and history, but if you are interested, you can read about it here for more context: www.mumsnet.com/Talk/childbirth/1401146-Coccydynia-and-second-delivery-what-to-do
Essentially though, I developed coccydynia during the 2nd stage of DD1's delivery (serious pain in the tailbone). Three years later I would say I'm 90% better, but another vaginal birth might reinjure the same spot. Then again, it might not and I've been busy assessing the risks/benefits of each mode of delivery for my individual case, which hasn't been easy! I'm slightly different to you in that, if I go for ELCS then it would be 'maternal request' so the perspective from my obstetric team is different (but I'm going on now about things that don't directly affect you.)
I think that the decision is actually made more difficult when you are who one who has the responsibility of making it! I completely sympathise with you; your desire to preserve your pelvic floor and avoid a repeat of the awful after-effects of PPH. Yet, there is no clinical suggestion that any of this will automatically recur.
It's just that you'd kick yourself if it did (that's how I feel about my case, anyway).
I think that I am perhaps ahead of you in terms of my thoughts regarding mode of delivery for my baby and I wouldn't want to influence you through my lines of enquiry/thinking. What I feel is right for me and my new Babba might not be right for you and yours. There is a book that I'm finding very useful at the moment called Caesarean Birth: A positive approach to preparation and recovery by Leigh East. I'm not recommending it because I think that you should necessarily go for an ELCS, but rather because ELCS is on the cards for you and you, too, need to weigh up the risks/benefits of each mode of delivery and decide what's best for you. The book contains information that is equally relevant to VB, and Appendix C 'the benefits and risks of caesarean and vaginal birth' would, I think, be useful to you.
There are in addition of course, the new NICE guidelines which might be useful. Here's a link that I've found useful: publications.nice.org.uk/caesarean-section-cg132/appendix-c-planned-cs-compared-with-planned-vaginal-birth
I too, would love a natural birth if I could be guaranteed that things will go smoothly. But, I have a previous injury that means I'm at a higher risk of doing the same damage again. This also means that there is a small chance that everything will be fine in terms of my tailbone ... which really only acts to muddy the waters and make the decision so much more difficult 
The harsh truth is that there are no guarantees with childbirth - which feels so much more true when you've already encountered problems. It's a risk/benefit analysis. I think that the key is researching your birth options and then being able to consolidate your findings by relating them to your particular case. Having confidence in your decision then is very important. My mind still isn't 100% made up (and I really need to hurry up!)
Good luck, and I hope that it all works out for you x I'll happy talk more if you'd like