Threesome

So me and my SO had talked about it a while ago and had wanted to do a threesome. We both agreed that both of us had to approve of the other female. I thought I had found someone but decided after getting to know her more she wasn’t a good fit due to her choice of partners and potential stds. We had moved on and forgotten about it and then randomly it came up again yesterday. I am bi curious and have wanted to see what its like fucking another female. Thinking about it gets me horny. I’m at a loss on how to go about finding someone that’d be safe (no stds) to do it with. Anyone who’s done it before how did you find someone?