i agree with ENIGMA (bouncing boobies

)...your body with adapt quickly when only using its own weight as resistence.....i suggest some bands for resistence if you dont want to use dumbbells or barbells yet.....
you could try some explosive pushups (trying to come up as fast as possible and actually coming off the ground each time) to increase the intensity..and try to incorporate some pull-ups and shoulder presses (hand stand position then lowering down and pushing back up) untill you decide to try weights
this should help your body get ready for the weights.......but i would eventually start training with weights...imo