I love the cover of this book on threesomes...
http://amzn.com/1592332714
Well, in your case since this is a gift and a little excitement for you as well, a threesome with a civilian would be more exciting. The reason I would say so is because at least you would know that the female is really into you and not following through because she is being paid.
At the same time, with a civilian your time is more flexible. You can meet up for drinks or if the connection happens, the actually session can extend for hours.
Good luck on your venture. I'd say get online and search. I once met a couple when "she" posted that she was looking for a lady to join them. There was a lot of flirtation that took place before we met in person. They sent me photos. They even had me listen in while they made love. By the time I met them in person, I already felt connected. She was absolutely gorgeous. He man was a Marine. Ahhhh pleasant time.
Stay positive and do not force it or you may end up with awful experience.