Sadly, doing exercises won't tighten skin or fat - it will only tighten/strengthen/tone muscles. You can provide some more support for your skin by strengthening these muscles, which can give you a more toned look (but doesn't take away the excess skin).

You could try speaking to a physio, or a trained instructor at your local gym about what you want to achieve. A combination of some cardio work for general fitness, toning and health along with some strength training for targeted areas might be what you are looking for. Be kind to yourself - your body has done amazing things, and yes, it will never be the same again. But you can do some work on it if you're feeling low in confidence - a word of warning though - don't believe huge promises, they're unrealistic and set people up for feeling even worse about their bodies. Small changes over a longer period of time are good to look for. Make sure you are eating a well balance diet too, nothing silly. Protein (like meat) is needed to build muscles so make sure you are getting enough protein if you start doing some strength training. And when I say build muscles, I don't mean like a body builder, you won't look huge or odd, just toned (and you might feel better about yourself if you make small achievements in your training each week).

Good luck!!!