It's a mistake to underestimate how much support you really need when growing. I thought that being small, I could wear a bralette or a soft cup bra. But I found that I suffered from "chest thumping" when using stairs.
I subsequently found that a plunge bra with a full underwire, some padding for uplift & nipple modesty, and especially with wide side panels was a lot more comfortable and secure. The plunge style is better than the balconette, as it allows more upper cup room for my nipple shields, which I really recommend that you try if you feel sore or wobbly.
Normally, bras in small cup sizes have narrow rear bands (with only 2 clasps), but I have noticed that wider bands are becoming available. I have just ordered a 38B with a 3 clasp deep back band and wide straps.
Frumpy, but supported & confident.