I had to go through "vetting" to see about a Roux-en-Y bypass. I was approved, but ,my insurance won't pay for it because I don't have enough health issues due to being overweight, I think.
I was on the fence about it anyway, because these surgeries are so drastic and I'd have to give up my beloved drinks such as diet Coke and watch what I ate so carefully. Also, I'd have to take vitamins. Otherwise I'd be malnourished.
I don't know about the gastric sleeve as far as vitamins are concerned. I'm sure you'd have to get a doctor''s approval. Unless there's a way around it I'm not familar with. If you want to do that, I think you could go to a surgeon specializing in those procedures. Even with that, I had to have psychological testing, attend a number of meetings to learn about the procedures, try out two kinds of vitamins to see which one I wanted, etc.
Best wishes, whatever you decide to do.