Sticking to the manual exercises

I have been doing manual programs like JP90 for a 1-1.5 year now. I gained 0.7 inch in length and around that in girth. I would like to gain another 0.5-1 inch in both length and girth but I’m kinda skeptical if I can gain that with manual exercises anymore. Is this achievable? I wanted to buy a pumping device but I’m not sure what to do now. I have no rush to gain it immediately but I don’t wanna waste my effort and time too. I’m open for all suggestions. Maybe I can combine bathmate with manual exercises?