Whatever you do is going to be a compromise. Wrapping yourself up well enough to give best endurance in the water will leave you sweltering and unable to safely operate the aircraft. I've seen someone suffering from heatstroke and it's not funny. When diving you put on the suit and get in the cold water, you don't put it on and sit in the sun under plexiglass for an hour or so.
One thing I'd really like to see is a spray hood on lifejackets. Floating is no good if you drown through ingesting spray.