You may want to look at neoprene spray tops (What Kayakers wear) 0r a neoprene rash guard (surfing shops). These would keep the torso warmer. A wetsuit would be overkill.

http://www.ronjons.com/ProductDetail.aspx?MenuGroup=8&SelectedItem=1&Category=Wetsuits+%26+Rashguards&Page=1&ProductID=1061-0042