Treadmills are a good warmup. They gotta do resistance training or they won't really burn anything. Pools are a great option because the water is about 7x the resistance of air. Fats with weights at the gym always worry me because their form is typically really bad and often they start too heavy. Like start with the physiotherapy type dumbbells, 2 or 5 lbs or whatever, and once your form and posture improve, move onto the heavy stuff.