Spot toning is ineffective at best. We all have problem areas, but what you'll find is that overall toning will aid all areas, not just those you're unhappy about. Go to the gym, and work your body totaly. Yoga is a good option because it engages a lot of muscles at the same time and is relatively low impact. Weight training is essential to weight loss though.
Also, consider your natural shape and the shape of your maternal side. Women are built in a variety of sizes and shapes, which for you might mean a little curve at the midsection. I began training for triathlons...running, biking, swimming and weight training (all over...arms, legs, core), and I lost inches and pounds. Even if you don't lose "weight" persay, the toning of muscles makes you carry your weight differently, which, if not reducing the size of your clothes, will make them fit differently.
Diet is of course important, but don't demonize foods like potatos and bread. Food is fuel, not a friend. Diets pushing one food group more than another are rarely effective in the long run. Go for balance and variety. Vegetables, fruits, meat (or protein if you're veggie), carbohydrates (YES EAT THEM!) etc etc etc. Changing up your meals does wonders too (IE, don't eat the same thing every day). Preparation also makes or breaks meals. Grilling is a great summer option. Baking in the winter. Avoid frying.
My trainer gave me the best wisdom for starting: It will hurt like hell for the first week, two weeks. But then, it gets better. It gets easier, it gets fun. You'll always go forward, never backward.
Have Fun
(ETA: Agreeing with the above poster than running really helped me see core definition)