I have rather mixed feelings about this issue. I had a VBA2C a number of years ago without a cannula or CFM. It all went fine, as is statistically likely. And of course, it is your right not to have them and still be cared for, although I guess in your case you may need to transfer to NHS care in order to exercise that right.
With hindsight though having since worked in high-risk obstetrics I'm not sure I would make the same choices if I were to have another baby. WRT the cannula: yes, they can be uncomfortable, and it's not nice having them put in but having been with women having them inserted in an emergency situation with a stressed anaesthetist, I would personally prefer to have one inserted under relatively calm conditions. You also need to be aware that they will NOT do a c-section without one in, so if you need one in a hurry there will be a delay while they get the cannula in. And the sort of emergency that requires a v.fast c-section in a VBAC is also the kind of emergency where it may be very difficult to get a cannula in.
WRT to CFM. NICE guidelines do state that routine CFM does not reduce perinatal mortality. However, afaik this is based on studies of women with low-risk pregnancies, not women planning VBACs where there are additional risks. I do not know of any good quality research comparing outcomes with or without CFM for VBACs. However, there is some evidence that the first signs of scar rupture can be detected by continuous monitoring. There was also a piece in the BJM this month postulating that although CFM hasn't been shown to reduce perinatal mortality, it HAS been shown to reduce the incidence of neonatal seizures which can lead to developmental problems. That's not to say that you can definitively conclude that CFM reduces the risk of developmental problems, but the opinion of the authors was that it may do and warrants further research.
As others have said though, having a cannula and CFM may increase your chance of needing a c-section and/or complicating the birth in other ways. It's up to you at the end of the day, you need to weigh up the pros and cons. I'm sorry that this isn't a positive cannula-and-CFM-birth-story, just thought I'd add my two penn'orth.
Hope it all goes well for you and you get good support whatever you decide to do.