Also check the support package offered - it isn't just about the operation, it is about the support received, guidance, dietician help and also psychological support - I have found the psychological support provided with my package essential and I never thought I would. The operation is on our bodies and not on our heads and we don't know how we will react until after the surgery. Make sure you are able to have that support in place somehow for after the op in case it is required - counsellors or psychologists. There is a lot of adjustment to be made to the new way of eating and it can be hard to come to terms with. That is without dealing with the reasons why you feel you need the surgery in the first place - your relationship with food - does that need to be addressed prior to the operation? Do you use food emotionally as a comfort, or a crutch? Do you binge, or over eat? (I am not asking you to answer this, just to think about whether you need help before surgery to deal with things).
Also, find out what is included for aftercare if something goes wrong afterwards either immediately or 6 months down the line, how will you deal with any issues? what will they cover? Are you limited to a number of consultant visits, or are you covered for a period of time eg. 2 years post surgery?
Or, if you do go abroad (I see you said you would prefer to stay in the UK), would you expect the NHS to pick up the pieces if there were problems?