Something more than a PFD is a very good idea. If you go into cold water without some kind of immersion gear, your lungs can be full of water from the gasp reflex before the PFD pulls you to the surface. I do all my kayaking in the (47-degree) open ocean and wear a semi-dry suit or a full wetsuit depending on the conditions I'm going out it. Dry suits can feel like a portable sauna in hot, sunny days and too many folks unzip them - which defeats their protection if you tumble in.
Folks on the Northwest Kayak Anglers forum swear by Gore-Tex dry- and semi-dry suits in all weather but I'm too much of a tightwad to plunk down that kind of cash. Sweating is much cheaper.
Northwest Kayak Angers sponsor tournaments and competitions and publish the minimum immersion gear you must be wering to compete. It's a good reference if you are just getting started:
https://www.northwestkayakanglers.com/index.php?topic=17843.msg192037#msg192037.
I hate to disagree with Evan, but a proper wetsuit (right thickness of neoprene) will keep you just as warm in the water as a dry suit, but dry suits are 100% more comfortable to wear. When I started kayaking, you could chose a wetsuit or a wetsuit. Recreational drysuits are a relatively new product.
A summer "shorty" wetsuit also reduces the chances of suffering the gasp reflex and are less restrictive than a full wetsuit, but you don't want to be too far from shore or separated from your watercraft very long because they're not the best at preventing hypothermia.
Whatever you chose, be safe out there.
