Hey Mathias,
I surf through the winter in Perth and down south occassionally and only really need a 3/2 steamer.
if you need any more than that, put a radiator on under the steamer and you'll be sorted. It's usually my hands and feet that get too cold in mid winter with the rest of it being OK.
In late summer I wear a 2x2 long sleeve shorty which is a bit of overkill, but I like it for sun protection as well.
in summer I just ride in a rashy and boardies mainly for rash protection and sun block.
See ya on the water,