To me being "naturally poly" means that you naturally can and do fall in love with multiple people without that meaning that the existing love or loves in your life diminish. Obviously if you want to translate that into the practice of having multiple loving relationships you can usually expect that your partners will have other partners too and that's where it helps to also naturally not be very jealous. However, even if you are a naturally jealous person it seems like for many folks it's possible to learn to manage it. Hopefully in time that will lead to you actually feeling less jealousy.
If you feel you are naturally poly but find that despite your best efforts you cannot manage or lessen your jealousy to a level you can handle then you should probably either practice monogamy or find a partner who's happy to remain monogamous while letting you be polyamorous (though that would kind of be a weird thing to set out with as a goal, as your monogamous partner could always change their mind in time and decide they want to practice poly too).
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.