Agreed with virtually everything written here.
Whatever you intend or feel, your post reads as if you're looking for a new car and found the vehicle that suits your purposes.
PLEASE: ask your self, what do YOU have to offer to HER? Do YOU fit HER specifications? How are you going to make her life better?
I would suggest reading some threads here about how
secondaries (which is what she would be, unless you're willing to demote yourself to being as equally disposable as a brand new girlfriend.) Also, do a tag search on secondaries.
I would suggest this thread about
dating a neighbor. The same issues are there for dating a co-worker. Perhaps more so, because it's often easier to move than to get a new job--not to mention the potential HR nightmare.
My own experience is that after 2 years of dating someone with whom I shared some work, and a weekly avocation meeting, he's ended up finally quitting the group to which we both belong, and I've fired him from our small business.
Consider looking into how long poly outside relationship typically last. Statistically, it's highly likely to end within a couple of years, and even more likely to end within 5 years. That means you're looking at a VERY high likelihood of dealing with these work issues, and things getting awkward and messy.
Read in particular,
newtoday's experience as a secondary. Consider the very real possibility that your husband may end up working with someone who feels much the same. You may end up knowing your husband is going to work with someone with whom he's fallen in love, and it might be just as much a struggle for you, as it was for her love's wife.
I honestly believe that as many secondaries get hurt by this...there are also a LOT of wives who were totally unprepared to see their husband REALLY fall deeply in love. The same thing happened to me, I believe. XBF's wife suddenly wasn't quite so poly, when she realized he saw me as more than a toy to entertain himself and shut him up while she was out with other men. Next thing I knew, there were constant 'change of plans' on her part, and I was expected to accept being groped in the back seat of a car on every single date. In short, she exercised a silent veto--just made things difficult for him and me until I got fed up and broke up with him.
Becoming friends first is good advice in its way. XBF and I were friends for 4 years before I got divorced. It's the only reason I agreed to go out with him. Not a chance in hell would I have gone out with a married co-worker who propositioned me to date him and possibly have sex with his wife.
But there's a flip side to dating a friend: part of the devastation to my XBF is the guilt he feels KNOWING that he hurt me and the even deeper devastation is that we WERE good friends already, and he and his wife have destroyed that friendship. He's lost my friendship, too, and that's devastating to him. He's OFTEN said in this last year that he wishes he'd never asked me out, because then he'd still have my friendship.
Consider, too, how these things affect your marriage. Are you ready for him to fall in love? Are you ready to no longer be the most important person in his life? Are you ready to treat this woman like an equal and valued human being with feelings, emotions, needs, wants?
As I asked at the beginning of the post:
What do YOU have to offer HER? How are you going to make her life better?
And last--if you even have to ask how to proposition this woman without creeping her out...well, honestly, that ought to say it all. Most women are going to be kind of creeped out by being invited to have sex with their married co-worker and his wife. And as someone else said, if this was really just about being friends with her, you wouldn't have had to ask. The two of you obviously want something else from her. [Side note: I'm pretty sure XBF's wife had some notion, before he asked me out, that she and I would be having sex and threesomes, and I still find it kind of creepy that she would even presume to expect that from me.]