I think it is easier to be "in the closet" about it with the Lap-Band than with any other surgery. If that is what you feel is right for you then I think you can easily pull it off.
I've lost a total of 47 pounds since I started considering the surgery. I'm loosing at a rate of about 1.6 - 2 pounds per week. It is a slow, steady weight loss that can be done without surgery (in theory anyway ... not for me personally obviously). But the loss isn't so drastic that it screams "I had surgery".
If you mom isn't supportive and she is a gossip then by all means don't tell her. It isn't anyone's business but your own. Who you choose to tell is competely up to you and you don't owe anyone any explanations.
Now I'm as open as can be about my surgery. There are very few people I haven't told. But that is because I was so excited to finally be doing something concrete about my weight that I just blurted it out all the time.
But my friends and family are super supportive and I didn't have any fears about them being anything but.
I do get tired at times of having to answer questions from people who don't understand that Lap-Band surgery is not by-pass surgery why I'm not loosing as fast. I do, ocassionally get tired of having a few people who are food police asking me if I "should" be eating something or looking at my plate to see how much I have eaten.
But so far being open about it has worked out okay for me.
I always, though, maintain the right to refuse to discuss it with someone or not to tell someone if I think they are going to be difficult or not supportive.