I have finally succumbed and joined a gym 2 yrs after dd was born, cos i am fed up loathing my shape (nice sized boobs but a tummy like i have a small koala in there). please - what is the best exercise i can do in and out of the gym to get rid of my post pregnancy tum, and is it worth getting those trainers that are supposed to do the exercise for you ? (MBTS are they called? v. expensive)