I know a bit about the Osaka scene for sure. Most of the hap bars and couple cafe are foreigner friendly to a certain extend.
The main problem that you may have is that they require a Japan issued ID (menchio, hokensho, etc) so you need to live in Japan. At least for the places that I know.
People tend to be very chatty and friendly so some decent Japanese speaking ability is always a plus. I've never tried to speak English there.
For what you're looking for, I would recommend "Kujira" in Tennoji. I've been there with my FWB and we had a great time, both socially and intimately.
We're not into swapping ourselves and people do respect that. So for as long as you're clear about what you'd like to do, this place should be perfect for the two of you!