I have just given up and gone for separates - the only one piece I have that fits is my entirely unflattering Speedo I wear for lap swimming and I had to go up two sizes from my usual dress size to get it to not dig in at the shoulders. They clearly design for people whose legs start just below their armpits.
I have the same issue - long body and massive tits, also currently breastfeeding. Almost all of them have foam cups - I'm baffled as to why. I bought one from M&S which did and it was impossible to swim in as the cups just absorb water - because they are made of sponge - and drag so it falls down. Fucking stupid.
I'm tempted by the magisculpt ones but only if the cups are removable. The Zogg one says they are but it only comes in sizes not cup sizes so I don't trust it to be big and supportive enough.
I'll be very impressed if someone can find a long body swimsuit with underwires and no padding.