I think you are not supposed to make them "look bigger" - that will just make you more shy, like; "Oh, what if people discover the truth...?"
The best thing is to be honest about it - and wear clothes that are honest about it. You'd be surprised how many good reactions you'll get. And even if someone should give you a dumb reaction, you'd be surprised that you didn't really die from that - you just know that that person is pretty dumb ;o)
But you yourself will much, much better when you know that they know - and it is fine.
So swimsuit: stretchy, rather than with pre-shaped bowls that are too big for you - nice colors that match your own (eyes, skin, hair) - perhaps some pattern or something if you prefer to distract attention a little bit away from your body shape. But people really do not "measure" each other that precisely, if there is an overall impression. That is much more what one goes by. And then your own feeling good also enhances your impression. If you feel free about it, people will relax - if you are all tensed up, trying to hide behind padding and everything, makes people "not relax".
And people prefer to relax - so everybody will be better off when you feel good and don't try to hide too much.