You really shouldn't eat less than a thousand calories/day. First off, it's just not sustainable and you are in this for a long haul so you need to be doing things that you can keep doing over time. Plus, you will hit starvation mode and the weight loss -- once water weight is out -- will stop.
The type of foods you eat does matter, and cutting down on the processing is helpful -- mainly in the context of salt. There is a huge amount of salt in processed foods. Check your Lean Cuisine labels and you will get an eyeful. I recognize that cooking all the time is not always in the cards but get yourself a slow cooker and you'll be better able to make more of your own foods, rather than relying on Lean Cuisine.
There's a million other things that can help -- go to
www.sparkpeople.com (I have zero ownership interest in that site, just love them) and see what they have to offer. I suspect you should be doing some strength training.
I know about long-term weight loss because I am in the midst of it. It is not easy, but you can do it.