Well done!
I would recommend squats for a great fat burning exercise, you can just use your body weight at first, then move onto holding the dumbbells as you do them. You can stand with both heels on books with your toes on the floor to aid your balance if you like. Keep your back straight and squat down slowly 3 seconds then stand back up 1 second, do as many as you can in one go then rest and repeat as many times as you can in 30 minutes, if you haven't done these before you will really feel it the next day, so make sure you don't have too much walking to do the next 2 days, but don't be put off, you will be surprised how fast your body will adapt and it wont be as sore when you do squats again.
Squats use large muscle groups which is what you want to do to burn calories, and they work the balance muscles as well, good luck!