Choose the swimming wetsuit based on the swimming style that you are going to practice. A thin suit (ca. 3mm) is good for breaststroke since thinner neoprene doesn't float or lift feet too close to the water surface, which would make the frog kick harder. A thin suit is also good for freestyle swimming. ->
How To Fit Your Wetsuit Properly With Paul Newsome (And Janine!) From Swim Smooth