I have a gastric bypass and had it in 2009. My bmi was 40 and I had no complaints comorbidities. My dieting history was well documented to the Drs and it w was my dr suggested surgery initially. Back then she applied for funding and got it simply, but things have now changed significantly (and rightly so).
Take a look at the nice guidelines for bariatric surgery but it is actually down to your local PCT as to what they find and the criteria - these vary greatly between areas.
Take a look at wlsinfo on fb or on the web as they are a supportive group of people who are at different stages in the process and can answer many questions.
You need to do your research for what would work for you and your eating habits. I would never have been successful with a band because of my habits. A bypass was the best fit for me (and 8st 7lb lost in under 12 months proved this to be right).
All surgeries can be reversed, but (except for the band to ) are significantly bigger and riskier surgeries than the original. However when I asked my surgeon he wondered why I would want to reverse something when the success rate is very high. Obviously it’s not plain sailing and not the easy option - meds for life, hair loss (in my case), and I have regained some weight (success is measured along the lines of 60% loss maintained at 5 years which I have done).
Bariatric surgery for dummies is a blood book and easy to read, the fat doctor was on discovery and follows patients having surgery, I would also strongly suggest watching the surgeries (yep in all the horrid graphic detail) so you really know what you’re getting into.
The surgery is the easy bit, the first week after is really hard particularly as your not hungry (which I never had before!). But (in my case) the weight loss was rapid and consistent and it was what I wanted. There are associated head issues with body thin, head fat (and this is super tough).
For me it was life changing and gave me significant (and unfair) opportunities as well as no longer being invisible (weird because I was massive!)
Good luck and feel free to pm me