Wetsuits are very flexible these days and very warm. I gave up my gortex dry suit a year ago. Got tired of fixing gaskets and the baggy fabric. I wear my Excel 4/3 Infinity Drylock for kayaking as well as SUP'ing, and even wore it on a photo shoot where I had to be fulling immersed in the water to get the shots.
What does 4/3 mean? 4mm in the chest, 3mm in the arms and legs. If you see 5/4/3, that means 5 in the chest, 4 in the legs, 3 in the arms. Around here in the Pacific NW, 4/3 and 5/4 are most common for surfing, winter paddling, and any open water trips. Recommended brands are Xcel, Patagonia, Mateuse, O'Neil, etc.
I wear Xcel 7mm booties, 3-4mm Glacier Gloves, and a neoprene hooded vest (Quicksilver).
Layering with a wetsuit -
I use a 4/3 all the time, but you can layer by adding a layer of capeline or poly pro under and/or a drytop over your top. I use a neoprene hooded vest which can be added if i get cold and the hood keep water from going down my neck. brrr. I wear the vest over the suit, some wear them under.
Dry suits -
Dry suits are waterproof garmets made from Gortex and a few other materials. Latex gaskets keep water from getting in the arms, legs, and neck. They keep you dry, but it's the clothing you wear underneath that keeps your warm. I used to wear fleece tops and bottoms in colder water temps, and a fleece sock. You can request to have gortex water poof feet to which are nice. Dry suits do require maintenance. The latex gaskets require spraying 303 on them every few days to keep them lubricated and from ripping. You should wash your suit after every use. The zipper needs a bit of paraffin (wax) rubbed on it after every few uses to keep it working. Dry suits fun from $400-$900. Popular brands are Palm, Kokotat, and NRS.
Different Options for Staying Warm -
A armless wetsuit called a farmer john is a great for warmer temps or if you're not planning on full immersion such as surfing. You can wear a fleece or poly pro shirt under the top portion of the farmer john, then for wind and water protection, layer a gortex dry top for your chest and arms. Dry tops are waterproof garments that are great to put over a full wetsuit, farmer john, or worn over rash guard to keep the wind off. Paddling pants are essentially gortex rain pants but with a neoprene enclosure on the feet to prevent water from getting in. Paddling pants can be worn over shorts, long johns, or even a full wetsuit. Reed Chill Chater, a UK company, makes light garmets that can used as tops, bottoms, full suits, and hoods. Their material is like neoprene but lighter and coated with a fleece layer. I have one of their tops for putting over a rash guard while wearing shorts in summer. It packs very small for storage.
Your Body Temp -
Everyone is different when it comes to staying warm. I tend to get cold easily, so I have 7mm booties, gloves all year, and usually a layer of capeline under my 4/3 most of the time. Friends shed their gloves in March, don't wear booties in summer, and some never wear hoods. Each his own. Follow your own direction, not your friend's. If they say it's warm, think of what that really means to you. Beware of the parking lot issue. Parking lots where you unload your gear are always warmer than the beach. Take a walk to the beach to confirm the wind and air temps prior to choosing your clothing for the day.
Carrying clothing on the board -
If I go out in my full wetsuit and the wind chill is in the teens or 20's, I'll bring along a dry top in a dry bag to be placed on bungees on the nose of my board. It's there if I need it. In summer, I may bring along the same bag to remove clothing if I get too warm. I may also put a pair of gloves or extra hood in my fanny pack for easy retrieval.
Sources for gear -
NRS - Idaho based kayaking and rafting outfitter. Drysuits, wetsuits, gear, etc, http://www.nrsweb.com/Default.asp
Kayak Academy - Seattle based kayak store for drysuits, http://www.kayakacademy.com/
Surf Ballard - Seattle based surf shop with Mateuse, Patagonia, and Xcel wetsuits, and SUPs, http://www.surfballard.com/
Urban Surf - Seattle based surf shop with O'Neil, Gath, and SUPS, http://urbansurf.com/
NW Outdoor Center - Seattle based kayak shop with drysuits, wetsuits, farmer johns and SUPS, http://www.surfballard.com/
Olympic Raft and Kayak - Port Angeles based kayak/rafting store with all gear and SUPs, http://www.surfballard.com/
Reed Chill Cheater, http://www.chillcheater.com/