hi lunshbox welcome....your now in the deep end of the pool.
I got here under similar circumstances a few months ago. There are lots of folks here that given lots of time and energy to helping those of us who are struggling. They have years and years of experience to draw from.
I would caution you and your wife to explore this more thoroughly than anything you have done before. Once you go through that door things are going to change and there maybe no going back. I'm not saying it is going to be negative or bad but things as you knew them will change.... if you and your wife don't like a lot of change then this may not be for you.
I think it might be a good idea to ask member who have gone down this road if 5% increase in happiness would be worth all the pain, and skull gnawing that is a result. Her 5% could cost everyone else including her 20-60% happiness in the short term. Right now my daughter and wife are at each others like a couple of pit bulls and I think it revolves around my daughter suspicions of her mothers outside relationship or affair, boyfriend.
I also think no matter how you feel today never remove the possibility of yourself having outside relationships. The reason I say this is during all the hypotheticals she can see things from all points of view. I don't believe that we "human" can control these matters of the heart. That said I believe no one can guarantee how they are going to feel once they fall in love and have a relationship....I was given similar assurances at the start....not sure how I would describe what those mean to me today. Good luck and ask as many questions as possible before going forward. Better to be sure this is something very important to her than some curiosity or whim.
Trust your gut..... D