You wear it every day and you spend more time with it than anyone else. It’s your bra and it looks like most of us have been wearing it wrong despite everything.
If your bra is too small, your strap will not be straight at the back and your cups will bulge out. Fix that by getting a bra that is neither too loose nor too tight. And don’t be cheap when it comes to your bra. As already mentioned, you’ll be spending a lot of time with it.
If you get a bra that has bigger cups than yours, it will look ugly under you shirt. If you get smaller cups, your breasts will bulge out of it and it will also look ugly. Make sure you get just the right size and don’t feel the need to lie about your size. Your breasts are perfect the way they are.
You can get strapless bras or opt for a bra with movable straps. Also, make sure your bra isn’t showing from under your shirt (unless that’s your purpose). Bras are underwear, they’re not meant to be seen at all times.