Just want to clarify I'm not a physio or anything...so what I'm telling you is based on my own experience as well as with trainers I've spoken to and met over the course of my training. If you don't want to build muscle mass then I'd suggest a program with lots of cardio work to build your endurance and to burn off a lot of the excess fat in your body (make sure not to burn ALL of it off - you need fat as that's what your body burns when you're exercising and recovering). It will take a little while but when you get into the swing of it your endurance will grow and your body fat %age should drop.
And for your weight training (which you'll need to do if you want to tone) focus on lighter weights with higher repetitions and more sets. Remember to mix things up so your muscles don't get used to the exercise - circuit training is great for the type of fitness goal you have.
And watch what you eat, of course.
