Hi.
It's a hard decision to make about surgery - I had mine at Guys and St Thomas' 6 years ago for arterial and neuro TOS but now have venous TOS and am having to make some big decisions too.
Where are you being seen in UK? You definitely want to be seen at one of the major centres. Have you only had the MRI or have you had any dynamic tests where they can see what happens immediately when your arm is in different positions like a venogram or something similar? From the MRI it seems like they can't be sure how significant the anatomical changes are so it probably might make sense to do some kind of functional test.
Might also be worth checking out the TOS facebook page - after 7 years, I only found it a few weeks ago and it's useful for getting feedback. Quite a few people from UK on it as well
Good luck with your decisions!
Jenny