I am a bi wife and have decided on monogamy in my heterosexual marriage. I'm baby bi though so my experience is limited. I have to young kids and my husband is tbm but treats me as an equal and I truly love him.

One thing to say... your wife's sexuality isn't for you. If you do decide to open up the marriage suggesting things such as threesomes as a way for her to explore while you to have fun is not a conductive way to facilitate her growth. It is very much a way for you to take advantage of it. If she wants to have one that is up to her to suggest. Honestly you might want to ask her if she is only suggesting it to appease you, if that is the case politely bow out of the experience, if she genuinely wants to then that's another story.