Get into a pre-bedtime routine and add some activity to it.  How about push-ups and sit-ups?  Or jumping jacks?  There is so much that you can do right in your residence.  You can start slowly and build up.  How about 2 sets of 25 sit-ups and 1 set of 10 push-ups a night?  This may take just 5 minutes of your time.  Always forget?  Hang a sign in your bedroom until it becomes habitual.  You can then increase the amount as you improve.