I agree the whole point of having another child is having a daughter.
That says it all, and is why you shouldn't go ahead.
But you're kidding yourself if you think a tiny girl won't be commented on. She absolutely will. My little sister was below 0% on the percentiles, she's tiny. It got mentioned ALL THE TIME. She's still a small adult, it is a drain. For her, it was a genetic glitch, an issue that couldn't be predicted. That isn't the case for you.
You can argue that small men may be more disadvantaged, and some people might find a tiny woman preferable, but I'm not sure they're the type of people you'd choose to associate your daughter with... But the bigger issue is that your sons are here. You have to help them cope because they exist. You'd be choosing to have a daughter with the knowledge you've got.
I'd imagine you've already researched where it's legal to gender select; so I won't go down that line of questioning, but there's a good reason not many places offer it.
Don't have another child. Focus on the ones you have; and supporting them. Get therapy to talk about your wishes for a daughter, because if you feel so strongly about it that you're willing to risk her having health issues you now know about; and pay for gender selection IVF, you're almost certain to have issues down the line if you do have a girl, where you feel either let down or you absolutely smother her and she pushes you away.
That's if it's successful. I only know of two people who have done this, both to have girls, and neither has a daughter. They both had pregnancies, one had several, but there wasn't a happy ending for either of them.