Survival suits are as good as the layers of insulation you have under them.When working offshore I always had several layers on, even if it meant sweating buckets in the helicopter and feeling uncomfortable in summer.
I sell lifejackets, both commercial and recreational. Many automatic jackets used for sailing etc can be fitted with a simple device that turns it to manual for flying. It takes seconds and is only a few quid. Ideal if you need your jacket for both.
Generally the manual jackets are cheaper but if you want to go all out for safety you can go for twin cylinders with light and sprayhood.
A good idea when ditching in cold water is a possibility is to have an external bladder with a breathing tube which allows you to take a breath from the bladder rather than a lung full of water during the cold shock stage on immersion. A nose clip is usually part of this product.
They are great for reducing the panic when attemping to exit a submerged craft.