Your obstetrician is currently failing you because she is ADDING to and not removing your anxiety over this.
This is NOT acceptable. It is technically breaching your right to the most appropriate care for your condition and this is what you should be focused on. You don't have a right to an ELCS, but you do have other rights which are important here and might relate to that.
I stress that whilst I say, you don't have a right to an ELCS, you certainly have a compelling case for one being the most appropriate care for your condition - which you DO have a right to due to your mental health. Mental health is a clinical and legitimate medical reason to have an ELCS.
Granting you permission to have an ELCS does not mean you are committed to having one. It merely removes that doubt and fear and empowers you to make decisions about your care without having to worry about the bureaucracy of this, which is actually contributing to the problem. Stress this. They are not taking your mental health seriously enough. They can offer alternatives options to support you in parallel with this decision which actually might change your mind. Indeed even if you have an ELCS they should be offering you this level of support anyway.
The NICE guidelines about antenatal and postnatal care can be found here:
www.nice.org.uk/guidance/cg192
There may be quite a few things in there that might reassure you or give you an idea of what they SHOULD be discussing with you if they have not already.
This includes discussions over whether or not you should take medication. (Stressing here, to keep taking anything you are, unless you have been explicitly told not to and if you are worried to raise the concern first and only stop with the full agreement of HCPs).
Mode of delivery is also very much one of those issues and should be part of your integrated plan with all members of staff caring for you.
Again here, if the obstetrician is not taking this into consideration and is not an active part of your integrated mental health plan then you are also being failed by the person who is supported to be coordinating this overall plan. There should be someone in charge of your care with this in mind - usually a named individual. In this case I would assume this is your perinatal specialist, so give them a roasting over it too.
I also want to stress something else. Whilst you have been advised that you are more at risk of postpartum psychosis it does not make it a forgone conclusion by any means. The fact you have been actively identified as at risk and are working with a team and are aware of the issue is massively positive and should help you. It might not stop it happening, but there definitely will be more help available, earlier intervention and you will get priority over everyone else because you are already in the system. This in itself reduces your risks in many ways. You are well positions to take positive steps to help yourself.
Keep doing what you are doing and being proactive in your approach and you are far more likely to have a positive outcome.
I would suggest that you possibly, may need to discuss whether there is anyone available who can see you at short notice during your pregnancy if your anxiety is getting out of control. It might be wise to discuss as a way to get leverage on the consultant tbh, saying that you are struggling to manage the uncertainty of the situation. Not being able to see your peri-natal specialist for another 3 weeks or so, is a worry. Perhaps approaching your GP too, for another one to support your case might also be appropriate as they too, should be part of your integrated care plan - if not now, but post-pregnancy when you are transferred out of maternity case.
I would also investigate whether there is any way in which your husband could stay overnight at the hospital immediately after you have had the baby. He is probably the person most able to recognise any changes in your personality, support you and your baby and advice health professionals of any concerns - more so than a HCP simply because he knows you best and has a relationship with you.
Because of the nature of your health, it may be possible to make arrangements that are not normal procedure and may not be on offer to other women. It is certainly worth asking.
My circumstances are similar but not identical (I'm not bi-polar) and was advised that I was at risk due to a history of anxiety issues (so they couldn't quantify by psychosis risk as easily). For this reason they were much more willing to 'bend the rules' for me, and I was able to stay on the high dependency ward in a private room with my husband following a maternal request CS on the basis of my mental health. Normally partners were not allowed on this particular ward and only on the low dependency one, but under the circumstances they felt that it was appropriate and manageable for the hospital to accommodate.
This helped to massively reduce my anxiety and concern over the whole situation, and practically was a god send whilst I was in hospital. Even though I was a high priority the reality is that the ward was ridiculously short staffed. They were brilliant but I think I would have struggled a lot more if DH hadn't been there.
FWIW I don't think its just about sleep deprivation in labour. You might want to think about this; you might be in labour for two days but be discharged very quickly after giving birth, but if you have an ELCS you are very likely to be kept in for a minimum of two nights anyway and getting any sleep on the postnatal ward is horrendous even after a very planned CS. (Even in a private room. You will be concerned and kept awake by the baby).
Its also not just about being in hospital. After you get out the first few weeks are difficult, possibly more so if you've had surgery. Give thought to this as well.
Think about how you can manage feeding. I was indifferent about breastfeeding prior to having DS. I was not adverse to the idea of formula at all - in part because of the issue of sleep deprivation. Afterwards I went a bit nuts about the whole things because of my hormones. An electric breast pump was a godsend in this respect and allowed DH to help me when I was struggling overnight and all logic and reason about formula had rapidly gone out the window. I really had not taken this into account in any way and didn't anticipate this at all.
Also I found a cosleeper invaluable, though this isn't for everyone. It just helped me make the most of the sleep I did have, and not have to get out of bed in any way to tend to DS thus making it much easier to get back to sleep when I needed. They don't tend to be cheap, but you can pick up second hand or if you do buy new, they hold their value pretty well.
Honestly, whilst I appreciate this might all add to the anxiety, it might also help to by identifying potential problems and how you might come up possible solutions about how you might cope with them before they arise. It definitely made a difference to me in the long run.
As I say, don't go into this thinking that you have a high chance of getting postpartum psychosis. You also have a 1 in 2 chance of NOT getting it - perhaps lower as you are fully aware of the triggers and are already planning for those - and to back this up, should the worst happen you have a high chance of getting good and appropriate care quickly due to you already being identified and in the system which a lot of women, even with bi-polar, are not getting in this country. Risk is not a straightforward measure and can be much more complex than a black and white number might suggest. Risk should be taken seriously but outcomes are not just determined by what happens but also how you and others react if things don't go the way in which you would prefer. In short, don't let something that might NOT happen totally dominate and destroy your precious time as hard as it may be; just don't rule out the help and support that is on offer for you should you really need it and seek out as much help as you can get.
GOOD LUCK