When I first got to my goal weight, at 25/26, my breasts were perky enough that I could (and did, when out clubbing or wearing halter tops) forgo the bra.
Second time around, I'd bf twins for nearly nine months, and there's no denying that they aren't gravity defying now at nearly 40. However, I wouldn't say they were saggy, and my nipples don't head south when I remove my bra
I do think genetics plays a big part in how your skin handles change. Also, I've always suffered with dry itchy skin and early menopause runs in the family. This has made me super vigilant about moisturising. When I cream my face, I cream all the way up to ears and down over boobs, and I have always, always used a ton of sun cream on my décolletage. I do believe it has helped.
All of the above said, I did consider a boob uplift a couple of years ago, but honestly, they have improved the longer I've kept most of the weight off, and also since I began exercising more regularly (press ups do help) and now I'm not planning it.
I REALLY urge you to delay the boob job until you reach your goal weight, or until you decide your weight isn't going to significantly change.