husband doesn't want me to have surgery
The way I look at it the surgery is to treat an illness (obesity) and would he tell you not to have surgery for cancer or a wonky gall bladder? If it were for vanity reasons and just because you want to look great I'd say rethink your reasons but it sounds like it is purely for health concerns.
If you are concerened about the Biblical issues of say disobeying your husband I would say speak with your Pastor because I'm not well versed enough in those areas. However if it because he is afraid for your safety or because he is afraid you will leave him when you get skinny (both common with husbands for some reason) then he needs to look at his fears and deal with them because they are not well founded.
I would never tell someone to totally go against their husbands wishes but I also see no reason to give up on something that will better your chances for a long and healthy life. See if he will verbalize what he doesn't like about the idea and maybe see if he will got to the surgeon with you to address his questions and fears.
Of course pray on the whole subject and listen for what God is telling you both, take time to address hubby's concerns and let him know you value his concern so maybe just taking the time to acknowledge his fears will put them to rest. Best of luck and God bless!