Well, here's my tuppenorth...
Get a neoprene suit, not a membrane,and make sure you get one with neoprene seals, not latex, much comfier. Augment that with a good thermal wicking base layer and fleece leggings and top.
Start with a nice shallow bimble and get used to the suit. Use your wing/bcd for bouyancy at first until you are happy to use either.
Oh, and don't forget to plug your inflation hose on it!
HTH
andy