Resistance bands can be used by people just starting out, despite size and despite limitations. I believe resistance training is key to weight loss. Plus, it’s a lot more fun than the treadmill! Here are some exercises that beginners can do.
Here’s a whole playlist of their exercise routines: http://youtu.be/K-iKrlw00Dw?list=PL9OZP636LDyV213H5FjIyzYQVGGoXb8r1
I got my resistance bands from bodylastics.com. (I have no other relationship to the company and receive nothing from them).