If you can afford a weighted vest it is better than a backpack but the backpack can work. I stay away from bodyweight usually because I prefer weights but plenty of people get results from bodyweight exercises alone. Also, if you are able to do so, do handstand push ups. It is the bodyweight version of military press and gives you a shoulder based workout that you are lacking at the moment. Just do a hand stand upside down and put your feet on the wall to avoid falling and push up and down. It is a good workout.