The water temperature will be between 80 and 82 - almost all year. There are people who get cold and you may be one of them. A lot of you thin people (I'm told you don't like to be called skinny) get cold in anything under 98.6. LOL I have to admit that this last week I resorted to a skin equal to 2 mil and was glad I had it on.
There are several options but basically a 3 mil will do - shorty or long. Although a hood may sound silly it is not. They actually make warm water hoods. The idea is just to not loose heat out through the top of your head. The other option is to add a vest over your 3 mil.
And the most important - which is very hard to get people to do - TAKE IT OFF AS SOON AS YOU GET ON THE BOAT!
Just because you get hot in a wet suit when it is dry does not equate to it keeping you warm when it is wet. Take it off and put on a wind breaker. You will be shocked at how fast that will warm you up.