Wetsuit (full) questions, any knowledge is helpful

I need a full wetsuit for Spring and fall riding, however if anyone can tell me what the difference between a 3/2mm and a 2/1mm wetsuit I would appreciate it. Is it basically the 3/2 is thicker and can be ridden in colder temp. waters?

Basic info about where I ride:
New Jersey, mostly rivers and bays at the Jersey shore. Temps while riding range from upper 50's to upper 60's, for the seasons I'm talking about. (I don't like to be cold.)

Thanks for the feedback.