Most of J's affairs have been with co-workers. All of them have ended well for them both, but there are plenty that don't. One has to be realistic about what the affair is about, the expectations of BOTH people involved. Be open up front that it is about fun and excitement, NOT ruining marriages, if it goes that far.
If you truly want to try to make this happen, explore this when in bed together and she is already turned on. Encourage her to dress sexier when she knows she will see him. Just flirting. Encourage her going to lunches with him, maybe even for a drink after work if the conversation comes up. Friends.
In our case, her first affair started because HE was coming on to her and she was enamored with the attention. That helped a lot. She didn;t have to be the aggressor, just the teaser. All I had to do was encourage her to "see where it went".
This is a much more feasible method of meeting people than believing the fantasies of chronic masturbators and OF sellers on the internet. Or hanging around in crowded bars trying to approach total strangers with the offer of "free pussy if you can watch"!!
It will certainly help that you have engaged in threesomes prior to the pandemic, you already know she is OK with being sexual outside the marriage..........but this changed the dynamic of meeting new people dramatically. One has a host of new things to worry about now, most of them don't allow for seeing your children grow up!!
Be aware, meeting people this way also involves EMOTIONS. On both parts. One has to LIKE a person before they are interested in becomeong more than co-workers, and then friends, and eventually Lovers. And while someone MAY agree initially to do something like this "for the fun", that doesn;t always carry over one the "fun" starts. You need a VERY stable marriage and more reason to stay married than you already are. I can honestly say that the only reason we STAYED married was our ......, and we are STILL married because we worked through that.
Think this out well before moving ahead. CW