wet suit sizing

I just got fitted for my pool classes and open water dives. The first suit I tried on was 3 or 5 mm (I think it was 5 mm). That was a struggle. But then I tried to put on the 7mm wet suit. First of all I couldn't believe how heavy that was, but putting that on was even harder than the first...

You would think after hundreds of dives and many different wet suits I would know the answer to this, but still, maybe someone has some good input. Be nice! My main issue fitting into a wetsuit has always been my athletic build. My chest has a tough time fitting a medium, but large fits like a...