I agree with CailinDana - go down the mental health route.
I'm not saying this is ideal, and given the whole issue of a woman's right to choose etc, it seems strange that you have to convince a consultant or whoever that you are mentally ill in order to get a CS -
However, from a purely pragmatic POV, it may be the most useful route to go down to get a CS. Arguments about family experiences of birth don't really count for anything - and presenting the pros and cons of a VB v CS as far as they apply to you as an individual might work, but only if you get a sympathetic consultant. It really is a lottery, and as others have pointed out, the guidlines are JUST guidelines. No one HAS to follow them.
Given that you are clearly very anxious about this, I would flag up urgently via your GP or consultant MW that you consider this to be a mental health issue, and ask to be referred to psychiatric services. They might well offer you counselling/CBT etc (which you can explore if you want to) but given that you are already pregnant, and none of these techniques are guaranteed to work, esp at speed! then it may well help you to get a CS.
I had a CS for my first due to phobic fear of childbirth. I had to get a recommendation for a CS from a psychiatrist. It was all fine, although ironically, it was still recorded as 'maternal request' on my notes. Which made a couple of MWs behave in a quite a hostile manner towards me (only a couple, I had a v supportive community MW and consultant MW, to be fair).