Well welcome Amanda, I hope our website continues to be helpful for you.
There's no rules about what circumstances and attributes you want in a new partner, as long as you're aware that more requirements = a lengthier search.
Looking for a triad would be a long shot because you'd have to roll the dice and hope the woman you found was (preferably equally) in love with you and Mike both. Not an easy proposition. But like you said, the triad thing is more Mike's ideal than it is yours.
So do you more picture you and Mike dating separate women separately? You seem to be less into the "emotional attachment" aspect of the outside relationship, where as Mike might grow quite attached to someone. Would that pose a problem for you as far as you know?
Is Mike worried that you will get "too attached" to a woman, and leave him for her? Perhaps Mike could spend some time thinking over what he'd need in order to feel reassured.
Check out our various threads, use the search and tag search features, and find out if there's anything you need to know. It's always a good idea to post your thoughts, questions, and concerns, I think.
So welcome aboard,
Love means never having to say, "Put down that meat cleaver!"