Is there any kind of basic guide for how thick a wet suit you will need is? I am doing my Open water Cert this weekend at Mermet Springs in Souther Illinois. The weather should be 75-80 and the water is listed at 82F droping to 75F at 20' and 42F at 40' as of last weekend. I am naturally warm most of the time but I need to pickup my gear for the dive don't want to be hot like in the Class/Pool sessions. Any Suggestions?