I can't help thinking that people who wear immersion suits are either hardened anoraks who fly alone (or in the company of other hardened anoraks), or they will very soon chuck the whole thing in.
It can't be much fun getting in and out of those things.
Flying should be enjoyable.
I am as flexible as any 50 year old can be but getting in and out of say a PA28 or any other single-door spamcan is a right b*astard of a job, that is if you are trying to do it without wrecking the seats you have to climb over. Doing it with a drysuit is going to be a lot of fun, especially if you have to get out in a hurry. I've got ~ 70hrs in PA28s so I know them well; they were designed for starved ex-WW2 pilots.
Much better to get a decent life raft, carefully brief passengers on what to do in the event of a ditching, and get it serviced regularly.
Plus carry a 406Mhz EPRIB of course, with a built-in GPS. They are quite cheap now.
BTW, in much of the Med there is very little S&R. Sure enough you will get picked up eventually (through the 406MHz-satellite activated commercial shipping network) but it could be days.
Whereas near the UK there is a chance of the S&R heli getting to you even before you hit the water; this actually happened to a Mooney (?) recently.