So my lady friend and I have been together for ten years and while we are having the best sex of our relationship currently and have every intention of continuing our commitment to each other, we've agreed that it is time to switch it up a bit sexually.  She's not into girls and im not into guys, so were thinking that a threesome is out.  However we are interested in seeing a foursome (us with another man and woman) would be the right next step.  There could be some intermixing among all four of us, but mostly were are imagining fucking in parallel so to speak.  She thought it would be better to find folks who do this as a service rather than taking the swing club route, theory being less risk for a new relationship forming.  Anyway, I bring up the subject for a few reasons.  First, I'd appreciate some recommendations as for a provider who does this sort of thing.  Second, I'd advice from folks about other things to consider (potential hazards, etc), particularly from folks with experience --on the hobbyist or provider side.  Board posts or PMs are welcomed.