try and get a hold of a heart rate monitor, and work out your weight loss range of your heart rate (or go by that your slightly out of breath but could still hold a conversation with someone) and then you will be able to go for as long as you like on what ever..... (i found this fine)
your trainer that you go and see will be able to help you but i think the calculations is 220- your age, that then gives you your max heart rate, so stick to 75% of that and you are in that zone..
but yes def get in some weight training, esp the chest ones as that will help you build the muscles around the area which will hold your new set of lovelys!!!