It all depends on personal tolerances and how much diving you intend to do. If you are just going to take a couple of dives, you'll probably be fine with a shorty.
I like a full 3mm suit and sometimes even wear something on my head. However, I dive multiple dives, multiple days.
Sincere question to all responders: Don't you guys find the dives that much more enjoyable when you aren't in the least bit chilled?