I am not sure if I will be much help here, but I will share my experience.
I wear a bra daily regardless of what I may be outwardly wearing. I am naturally a small B cup, and have found going braless to become uncomfortable especially as my activity level increases. I will also generally wear forms to fill out the cups for a better fit. This gives me a solid B cup or small C cup bust line which on my frame (6 foot plus, 300 pounds, built like a bear) is on the smaller size.
The style of bra that I wear is generally dependent on my plans for the day. If plans call for more physical activity, I will wear a sports bra, but otherwise my goto bra is usually of the fully lined underwire style.
As I said earlier, I do wear a bra daily year around. I would doubt if no one actually noticed, but no one including my family has not said anything to me.
I apologize for the lack of polish on this post. However, I formed the response as flow of conscious while multitaksing.