S.,
I haven't had a C-section, but have had about 45 lbs of extra weight to loose. I have been using the Momentum Fitness System by Jonathan Roche and it has been great! I have lost two dress sizes in a little over a month. He combines heart rate intervals with core exercises, this includes your lower abs. By working with your heart rate you slowly increase the difficulty of your interval workouts over time as your body adjusts.
Usually I hate to workout, but now I look forward to it every morning. You can either buy the system with the heart rate monitor (suggested) or without and just use exertion levels as your guide to the interval intensity.
I hope this helps. Here's the website so you can check it out. http://www.momentumfs.com/
You can try out the system for free. He has a section for free workouts and core exercises and if you like what you've tried then you can buy the system outright.
Even better, if you go with the on-line recording system, you earn points for recording your workouts and track your weight. These points can be used towards workout equipment, water packs, sunglasses, etc.
If you do go with the system please write me down as your referral, I get extra points and have been saving for a nice hydration system.
Good luck with your weight loss!
-C..