As somebody the teaches HUET and sea survival I can't stress enough the importance of lifejackets and TRAINING.
It's all good and well to go and spend your hard earned dollars on a raft PFD's EPIRBS and so on but unless you have been trained to use it in an emergency you have as much hope of doing it right as I do of ever getting the money to finish my PPL.
If you are operation over cold water you need thermal protection
Here are two videos I use in my courses regarding cold water:
https://www.youtube.com/watch?v=_96YEPAdA2Y
https://youtu.be/_96YEPAdA2Y
Cold water PFD
http://survitecgroup.com/products/shark-lap-jacket
Warm Water
http://survitecgroup.com/products/mk28-passenger
Spend the $450 and do a HUET course of you are operation over water on a frequent basis.