while all the above feedback is correct, one must also put the risk into a statistical framework. The brightest minds will tell you that the percentage is very small to pass on HIV from OWO. Of course there are other STI's along with that remote possibility of HIV but if it were a big risk, prossies in general would not do it. They are just as concerned about getting something as you are.
Compare it to getting on an airplane, the probability of getting into a crash is unlikely but if it happens then there is no comeback even though planes are safer than cars. Does this stop you from flying?
to provide perspective with my own experiences, like yourself i was concerned about STI when i first started punting 14 years ago. I started out OW then slowly moved onto OWO in my first year of punting. Today, everything is on the menu. Knock on wood, I have never caught anything. I was last tested 6 months ago.
Im sure there are other punters on here who would say the same but you just have to size up your risk reward. My personal suggestion if you are single, take the risk with OWO and CIM bc its an amazing feeling getting a porn style BJ; life is too short not to experience this. the likelihood is very low you will catch something. if you get into a relationship, then thats definitely a reason to prefer OW. since being in a relationship, i still do OWO sometimes but i have cut down my punting from 2 to 3 times a week to once a month with the goal to give up punting completely.
Above all else, do what makes you feel comfortable.