The easiest way to break the ice is to "stumble" upon a video online about polyamory and watch it with your partner, and then ask what she thinks about that kind of relationship style. Introducing it as a hypothetical / abstract notion lets you test the waters without putting pressure on her to "say the right thing."
From there, if she seems at least a little bit receptive, you can tell her exactly what you've said here, in whatever language is comfortable in your relationship.
An important thing to remember is that you've been thinking about this for a while, but you're just presenting her with the idea for the first time. So be patient and allow her to mull it over at her own pace. You've been consciously dealing with jealousy issues, whereas she's been in a comfortable monogamous mindframe where she could just ignore those feelings rather than deal with them.
Some people never fully get over jealousy, and that's perfectly fine. What's important is to take accountability for your feelings, not to blame them on someone else, and then learn to just be at peace with them. For example, everyone has bad days. When I'm feeling down, I don't try to change the way I feel, I just try to be conscious and aware of what I'm feeling, what events may have triggered these feelings, and what thoughts I'm having that caused me to react to these events in that way.
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker