I have worked out my favourite bra type, but buying a new bra which suits is still a challenge.
I am now a B, going on C cup and I project my pointy bits, well, quite firmly. Braless, I quickly feel heavy, and stairs give a nasty "thump".
I find that a lightly padded underwired plunge bra gives me the best fit, modestly and shape. Unpadded and non-wired bras tend to mold rather than lift, and I don't feel supported in them.
I look for bras with deep side panels and 3 hook bands. I find this gives much more support and side pushup. The deep bands generally are designed with "leotard backs", which gather the straps towards the clasp. This means your straps are unlikely to slip off.
Curently, I am looking for bra styles where the strap buckles are located near to the bra band, rather than on the shoulder. This will help in being under-dressed in just a tee shirt plus bra.