Write things down before the appointment! I found that I struggled to articulate things or forgot important points, plus writing it down was a good way to actively demonstrate the thought I'd given everything rather this being some kind of flight of fancy.
It also helps you to think of responses they might come up with, including tactless ones, so you can prepare yourself in case it doesn't go how you hoped.
My approach would be to stress the following:
You desperately would like to ttc but your anxiety over childbirth is proving an obstacle and you need help with over coming it.
Whilst you understand that an ELCS is a serious operation and you do not have a right to one, you would like to explore this as a way to deal with your anxiety over becoming pregnant as you feel that you could cope with it better.
You are worried about panic attacks inhibiting your ability to consent so would like to give birth in a way that is as controlled as possible, understanding that at times things can and do go wrong for all types of birth.
You want to take action now as you are aware of your age being an issue now and that you have not got time to go through years of counselling on the subject.
You are open minded about counselling and see that as part of the process even if you do get an ELCS agreed in principle.
One of your fears is about not being taken seriously and not been treated with respect as a result of your fears.
That the process of getting an ELCS agreed only after you are pregnant is too much for you to cope with. You could not go through with a pregnancy under those circumstances.
My understanding is there have been slight changes to NICE guidelines relating to mental health since I went through this a couple of years ago which are relevant to your position.
The recommend that any women who is considering becoming pregnant has the opportunity to discuss this with HCP if she has mental health issues. I believe its supposed to cover women primarily who are taking medication or have severe problems but its not explicit in this, and does therefore apply to any woman who might have severe anxiety over childbirth. If you have a history of anxiety problems this might work to your favour too. They should listen as, unfortunately, if you have mental health issues before pregnancy you are more likely to have problems like PND after so they are beginning to take requests for help more seriously as it can help reduce problems and it gets you into the system as a vulnerable person in need of extra support regardless of how you eventually give birth (despite this being at times frightening or just a pain in the bum, on the whole its a good thing. Midwives are more likely to spend that couple of extra minutes with you because you need it).
The services that do exist for women ask for an ELCS tend to be geared up more for women who have previously had a traumatic birth. Women who haven't given birth, do find it harder to prove they have a legitimate problem that needs help and support, but as I say things are beginning to change and I was able to do it.
This does mean that as a none pregnant woman without kids you are at the bottom of the pile for a referral as you are not considered a priority (tbh, this is quite right) and demand for services does out strip supply, so you might have to wait. But it doesn't mean you don't have a legitimate need for those services either.
You might find they will only refer you to counselling initially. You might have to go along with that as part of the process to demonstrate that you have explored whether this will help. Personally I have a few issue with this need to prove your case, but I also can see why its there too. And actually with the benefit of hindsight, I recognise that I did need emotional support in my pregnancy about my wider anxiety (unrelated to actually giving birth) and having some help with that.
If you go in with the attitude that this is about getting mental health support and you feel an ELCS would be a useful tool in achieving that rather than merely demanding an ELCS, you should get a better response.
If you understand what the system is setting out to achieve and why they have the system there is in place, it does help to navigate through the ignorance and prejudices that do still exist around the subject - even from those who work in maternity. Things have come a long way in the last 5 years or so though since the current guidelines were drawn up and there was a recognition of the problem by NICE.
You still might have a negative response; please just see it as a setback and part of the journey. Equally your journey is about having a healthy mum and baby at the end of it, not just having an ELCS. Mental health is a legitimate health concern. This is a legitimate reason to discuss pregnancy and childbirth with someone who can help you with your mental health during that period. Don't let anyone tell you, or make you feel its not legitimate as it is.
You have just completed step one of the journey though - recognising that this is a problem that you need help with and are seeking out that help. It takes more guts than people realise to admit that. You are brave despite your fears in trying to find a way to overcome them.
There are a number of women on MN who have been through it, like me and like Annie is currently going through. It can be hard to talk about in real life. But MN is generally a safe space for support with it.