I hope you do not let that stop you from posting and/or feeling welcome. The beauty of a forum it is great for many things. The curse is that some people might some judgemental or highly opinionated. That is the drawback. You have many personalities mixing.
As someone who has been poly for many years, I guess my one piece of advice is that when you are exceedingly specific about what you want, you limit your options. You have to be mindful of how you phrase things. What do YOU have to offer this person? What does your husband have to offer this person? What kind of relationship are you seeking? You have to take into account that she has wants, needs feelings, dreams, wishes, hopes, etc. How you approach or phrase what you are seeking can determine a person's reaction.
Unicorn hunters or married couples who seek a third person to spice up their relationship are frowned upon. You are on the odd end of the poly spectrum with what you are searching. Know that there is nothing wrong with what you are looking for. It is one of those things where you should take heed and actually absorb what people who have experienced it actually have to say. Too often, that third person ends up getting the short end of the stick or a bum deal. They start feeling inferior because this marriage or long-standing relationship has been in place for 5, 10, 20 years. It poses the question of, "Should a person who has only been here for two months have as much say or as many rights as person who has been in the relationship/marriage for 20 years?"
It is nothing personal, so let it go and take it with a grain of salt. I skimmed through your thread, and the advice that was given by a member was that instead of seeking a person, you should get a pet. What I took away from that is that you should think about what you have to offer that person, and would they be getting a fair deal? You said that you and your husband both travel. That means that she would have to be accustomed to one or both of her loves being away at a time. Would this person be able to have other loves outside of you and your husband? Would this person be with him while you are away and vice versa? How would it work upon your return or his return? How would timing issues be worked out. You have to consider time constraints as well. I am sure the poster did not mean anything negative. I took it to mean that you have to think about those things before bringing a person who has feelings and needs of her own into it. That is all that I took from it.
There are some good people on here, so I do hope that one response that you did not particularly favour or care for will not stop you from seeking further advice. Most people on here are very honest and blunt. They do not tell you what you want to hear. They tell it like it is and what you need to hear but probably never wanted to hear. I appreciate the tough love from time to time. Sometimes I need that. Either way it goes, I sincerely wish you well.