There are several m/f couples that post on CL and elsewhere. Since they are a provider team, they follow your instructions. If you want a str8-only experience, then it will just be you and the male provider fucking & sucking the female team member, with no homosexual/bisexual activities involved. Some of these provider couples state that they are 100% str8 only.
I had one mfm swinger experience years ago. They were a French couple who live in NY. He was a chef (stereotypical, no?) and she spoke no English. She wasn't what I'd call hot, but not horrible. She was very into it and compliant, but the language barrier made the experience a bit less than ideal. She did not speak Greek, so the action was limited to one of us getting sucked while the other fucked her pussy. Well, it was free, anyway! They actually requested a repeat performance, but the lack of communication with his wife was too big a turnoff for me.
In any event, I intend to try a str8 provider couple soon. I will report back if this happens.