Surf, dive, sail and paddle sport shops may offer better prices than aviation outlets.
Neoprene has various thicknesses depending on expected water temperature. You want fabric on both sides. Neoprene has to be worn next to the skin and once worn needs immersion to keep it from becoming aromatic. You will quickly know how cold the water is when you enter it in a wet suit. It takes some time to warm up.
Dry suits and tops with suitable layers underneath can work out.
A dry top can keep your body core warm enough to sustain the effort to get into a raft. In the channel it may sustain you long enough for the rescue services to find a live body.
Trans Atlantic may call for the full version.
Check
EQUIPPED TO SURVIVE - Outdoors Gear, Survival Equipment Review & Survival Information for real world ditching stories and raft tests.