Hoods
A significant amount of body heat escapes through your head, and cold water in the ears is what leads to surfer's ear over the years. Neoprene hoods and caps from Mystic and ION in 2mm and 3mm.
A separate hood is more versatile than a built-in one. You can add it on the coldest days and leave it at home the rest of the year, rather than committing to a hooded suit that is too warm for eight months. Look for a hood that tucks under your wetsuit collar, which stops water funnelling down your back.
Fit around the face should be snug without restricting your jaw. See also neoprene beanies for milder days.