Husband and I want to have a threesome

My husband and I have been together for 12 yrs and have recently been discussing having a threesome. It has always been one of our fantasies and we are both fairly young. The real question is how do people even go about finding a third person for a threesome? We cant tell our friends due to the judging that would take place, but then again we cant do this with a stranger because we dont trust not getting an std or sti. Its like we want this, but we want to do it safely 🙄