Has anyone crossed over a friendship line and actually discussed this with the other person?

There’s someone I’ve gotten to know over the past few months and through I was very interested in the beginning, I feel now we are much better as friends. Problem is, he’s still hot and I’m still horny..... I’m pretty sure he’d be up for it too. How do you start that FWB conversation? What are the boundaries that need to happen?

Ps. We are both mature working adults. Looking for real thoughtful advice from people who have actually had a mature FWB relationship please!