Just as you have different jackets, you may need different suits. For very cold riding, a drysuit makes it warm. The baggy suits allow you to wear sweats underneath for warmth. The next step is a 4/3mm wetsuit. Wetsuits allow water in and your body warms it up and the suit provides insulation from the cold air and water. During colder water, I squirt warm water into my suit before I get in the cold water so it is not as much of a shock. There are also 3/2mm wetsuits in short and long versions. Great for cool conditions, but you will not overheat as with the dry or 4/3. Then there are skins 1-1.5mm shirts that keep the chill off for the early morning sets. My website has has illustrations of each.
www.boarditup.com There was just a discussion regarding Adrenaline Drysuits on this same board you should read.