I would not even consider worrying about other's opinions. Wear what you feel fits correctly. Not all men or people want to see huge mamas falling out anyhow. I actually prefer flat chested women or small breasts and I am sure there are many men who would appreciate you for the person you are and the way you look dressed in any type of clothing. Don't go through life worrying or thinking about what other's think. Their opinion/advice is worthless. Be yourself, look for others like yourself, see what they wear. Don't set your standards by famous people or the mainstream, in style. That is boring and cliche. Do your own thing, stand out on purpose. Let people see you don't care what they think. How do you think people get noticed, in a good way... they are different. Lady Gaga, Britney Spears, but not just famous people. I was never a fan of swimming in school because I was a thin boy and felt a lack of confidence. I tell people that they should not care what others say or think. Most likely those people are fat and nasty anyway. Being flat chested is nothing to be ashamed of. I see your age is 18-24, so I am guessing you will develop over the coming years. Do an online search for bathing suits made for women with small breasts. You may find many stories and advice from people just like yourself... look up videos as well.
Any kind you want. Bikinis look good in general, and no one is going to think less of you because you wore one even if you aren't very top-heavy. don't worry about whether you have boobs or not. Just find a bathing suit you like, that you think you look good in, and go to the beach/pool/whatever.
It's a good thing that you have itty-bitty titties, cos you can wear any style of bikini you like and you'd still look great! It's the busty girls who'd have troubles getting a bikini top that fits and enhances their body. Go for a halter-neck bikini or racer-back swimsuit that accentuates yourself ☺️
Forget about it. Wear what you want. Lots of guys find small-breasted women attractive. There's a new woman at work, very tall, thin, not curvy at all. Cute as can be. It's a treat every time I see her.
I have this problem too, (although I actually don't mind it) and I find the ones that are a sportier cut more like a sports bra work better. But then I typically go with a one piece anyway, because I'm a dancer and they feel like a leotard.
You should opt for push-up styles (I know Victoria's Secret has a great selection) to feel more confident. Or to distract from the size of your chest, try tops with details (e. g flounces, crochet, floral details).
Or if you just want to avoid attention completely, go for the "halter bikini".