Sam,
I agree with Nat. Start slow, keep it simple. Also, I recommend scheduling a time to do your exercise. My recommendation is to get it out of the way as soon as you can in the morning. This helps because you are less likely to make excuses to blow it off later in the day. Studies have shown it takes about 6 weeks for an activity to become a habit - get moving and make exercise your new habit.

Regards,
Lux