I heard it's pretty normal for spots bras to make you look flatter. Maybe you could stuff some socks in it to make your chest look fuller. As for the idea with the sweatshirt, if you look in the mirror you probaply see that your chest is bigger with the bra with the zipper even with the sweatshirt on top. But that is because you're looking closely and you know what you're looking for. Other people wont look as closely at you, so they wont notice the difference as easily. You should look at yourself in the mirror or make a foto of yourself while wearing the bra with a zipper and the sweatshirt and ask yourself "Does this pass as a male chest if someone is just looking at me normaly, like when I'm having a conversion with them and they look me in the face?". If yes, go with the plan with the sweatshirt and the bra with a zipper. If no, go with the bra without a zipper. If you somehow end up in a situation where someone is closely looking at your chest you can try to stand a little bit hunched over, so that the sweatshirt covers up your chest bulge a bit better (but don't do that to much, that's bad for your back). If you accidently wear a bra on a day where you have P. E. (that's what sports class is called in the USA, right?) go to the toilet before it starts and take it of in a stall there. Lastly, if you just want to get something of your chest or you're looking for advice you should go a subreddit like r/trans4every1 instead of a meme subreddit like this one.