Yes you can request one. You need to ask your midwife or consultant about it.
You do not, however, have a 'right' to one. The NICE guidelines support women who request an ELCS - most specifically on the grounds of mental health - but they do cover other concerns.
The big issue you face, is the reaction you will get to a request. Some hospitals and some consultants are very hostile to them. Indeed despite the guidelines there are a couple of hospitals who have a 'blanket ban' on maternal requests and some HCPs are actively opposed to them on ideological grounds. Equally there are some hospitals which will have no issue with such a request. Its pot luck, and largely about how much you want an ELCS.
I always say to people considering doing this, to think about various alternatives to an ELCS, as an ELCS isn't necessarily the best solution for worries of this nature. It seems be being pushed as a solution and there aren't many other suggestions being promoted when they may be more suitable.
I think its worth pointing out that even though you are measuring big on your scan, that they are notoriously inaccurate and unreliable, so you may well be concerned over nothing. And that if you DH is supportive he can be educated even if he doesn't know anything. Failing that, using a doula may offer that support that he can't.
In short there is no right solution here, only one that is right for you.
I would also echo other poster's concerns about your low blood pressure though. They monitor this throughout surgery as its something that can cause problems. I would not assume that it would be any less problematic to you as labouring for that reason. If anything I would suspect that its more risky, but you'd need to get medical advice to be able to assess that in your personal circumstances.
I'm not trying to put you off in anyway, but I think you should be aware that this can be a battle and you really should explore a number of alternatives just in case.