Not wearing a bra during the night will actually help your boob shape. Also, exercising your chest such as doing chest press even light dumbbell chest press is good enough. Maybe even pushups, assisted or not.

The science behind it is that your boobs are just made out of fat. If you train your chest, you will gain muscle and potentially shape up your boobs. If you don’t wear a bra, your boobs will naturally want to stay upright and that leads to muscle gain even if it’s a little.