I'm rather gifted up top, so this may not totally apply to you (but I need lots of support, and it seems that's what you're after, too).
I wear a supportive bra (moisture wicking) with my tight tri top over it (tri top is a waist length tank, but very tight). I swim in both because when trying to get anything on your body in T1 while wet is impossible/frustrating/irritating (IMO, anyway).
If you swim what you'll bike/run in, it makes things much easier. I always use body glide and don't have any chafing problems.
Good luck finding a combination that works well for you.