A lot depends on how long you have been large, genetics, age,etc.
ANytime we lose a large amount there is risk. Most of us who were sort of 16 stone or larger seem to have some issues - I was 20 stone, and have more then I want.
Toning along the way should help- swimming seems to be a good choice as it uses all muscle groups. Firming creams are out there, but I am dubious of their success rate.
Bio-oil will help with stretch marks, but not much for shringking skin.
It is supposed to take many months after a loss for skin to return as much as it will, so be prepared to live with it for awhile, hoping for the best.
I am 7 months post diet, and still have a problem. In fact, in some ways it is worse then when the diet ended.
When I can afford it, I will have surgery, as I don;t think mine will go to a satisfactory level....I was obese for 25 years. Thats a lot to ask of my skin, to shrink back after all those years.
Lots to consider. Good luck to you!
x