Learn the French G perms. Then I would actually try learning ZZ. I used ZZ for a little bit on OH and still use it on a few solves and it helped me improve my RUL TPS and it also gave me a better understanding of the 3x3 as a whole. You don't have to continue with ZZ but learning it can teach you a few techniques that work well for OHHello. I avg about 25-26 seconds on OH currently and I believe that I can I improve upto low 20 seconds simply by practising as this is what I averaged before quiting cubing for almost 1.5 years.
I am aiming for sub -17 on OH now. My method is CFOP. What can I do to improve further? I mostly use 2 look OLL except for some cases and 1 look PLL except for G perms.