50° will be a lot different than 70°. As stated, cotton is horrible.
poofy warm isn't a good warm. Poofy is squishy, and squished it isn't warm. Thinner, but denser, has proven to work better for me. Doesn't squeeze as much. But under the right conditions can work.
Out of my personal collection of undergarments (have several) I would be running the 4th element halo in 50° water, this is a good choice in 50° SoCal waters. The Wenzel compact in 60+° water. The Wenzel is squishy, but works pretty good in warmer water where I don't want to be super warm. I have a little bit of a thermostat with more air added to the suit for more warmth and less air to run cooler. Variable poofyness. Some fleece for the 70° water.
Depth, duration, thermoclines, and surface temps also doctor what is a good choice. Not a bad idea to run a little chilled for a short dip below a cold thermocline to avoid overheating in the shallows/surface.
Too much warmth, I sweat, get the undergarments wet, then cold no matter what. I've been more comfortable with less undergarment than too much.