(Yet another) Advices for "The Talk" to open our relationship?

Hello Redditors,

I (27f) have been with my boyfriend (31m) for eight years, and I have been thinking about opening our relationship.

I started thinking about it about few months ago and took time to read and research the subject (The Ethical Slut book helped me a lot to understand what I want and expect, and why I feel the need to open up). Now it's time to talk to my boyfriend about it, but I don't know how to start the conversation.

We have an awesome relationship. While we are both rather emotional, we have only had one fight so far due to a misunderstanding, and we were able to easily work things out, so I would say that our communication is great overall. However, he is shy, and I really don't want to scare him. I love him deeply, and I want him to understand why I think it would benefit us both, even if he refuses in the end.

I have searched through different subs to see how people bring it up, and the most common way I found is during a calm pillow talk. The problem is that we stopped sharing a bedroom four years ago due to different sleeping schedules, sleeping preferences, and his heavy snoring (was one of the best decisions for our relationship), so pillow talk is out of the question. We also don't have any friends or people around us who are ENM, so it's difficult for me to broach the subject. I believe he's smart enough to understand why I'd suddenly bring it up, given that it's something we've never discussed, I am thus thinking about jumping straight into the topic.

Do you have any advice or experience that could help me work out how and when to bring it up? Any wordings or situation? Ultimately, it's his decision, and I won't force him or try to convince him to do something he doesn't want to do if that's the case - yet I got no clue about how he will react. However, I need him to at least listen to my arguments, so that he doesn't feel threatened by my suggestion. I need to reassure him that it's just an idea, an option, and that I don't want to break up or cause any trouble. I also think he deserves to know this side of me out of pure honesty.