You've got a few options:
-use harder exercises (wide-grip pull-ups, ring pull-ups, ring push-ups, muscle-ups, dips, handstand push-ups)
-use a weight vest or back pack (this works fine, but you'll need to use REALLY strict form and the load will shift on your back)
If I were you, I'd take your current simple-fit workout and put on a back pack or weight belt. Then concentrate on maintaining your current number of reps while adding a single pound every week. A year from now you'll be pushing around 52 lbs and will be a hell of a lot bigger and stronger. You may have to reduce the weekly workouts to two if your gains slow down. Google John Christy to get pumped up about micro-loading.