Your Experience: suit sizing across brands

Hi, Help me out-- I need to buy a new suit but don't want to drag a fussy 2 year old all over town trying them on, only to order one online. In the past I've always gotten the Nike 100% polyester tank training suit. They are fantastic and last several years (until the seams rip) but for some reason it seems like the cut on the last two ones I've ordered has been a bit high in the bottom (they tend to give me wedgies) and a bit low in the front (exposing more of my modest cleavage than I'd like to). I am a size 30 in these suits. (Am 5'8", 130 lbs) So I want to branch out. I've noticed that Dolfin is now making some 100% poly suits that aren't too expensive. Have you tried them? Liked them? What size would I be in a Dolfin brand suit? Do you have some other favorite suit that lasts forever and could recommend a size for me? I don't want to waste money on any lycra/spandex because those fabrics only seem to last 3 months in my pool. Thanks! ~Samantha