Courtney Stodden is going under the knife tomorrow to scale down her breasts ... and the operation has a lot of significance for the model.

In an emotional Instagram post today ... Courtney lamented how emotionally scarred she is from being married at 16 to actor Doug Hutchison, who was 35 years older. She noted that the ceremony was 15 years ago today. The wedding took place in Vegas, where the marriage was legal with parental consent.

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As TMZ reported ... Courtney is downsizing her melons ... and she says of the decision, "For the first time in my life, my body feels like it belongs to me instead of the public that consumed it before I even became a woman."

A source close to Court tells us ... the bazongas aren't going away entirely -- they'll just be more manageable -- but still a handful! BTW, Courtney got the implants in 2013 when she turned 18 ... which we're told was done to feel like a woman, and not a child amid her trauma.

Good luck, Courtney!