My opinion is that shell suit is definitely the way to go. The warmth comes from the undies not the suit - even though there is some truth to the fact that neoprene gives a little extra barrier especially the moemnt you enter freezing water.
Neo suits are a drag: Heavy, pain to dry (I see you are from England, I've lived there, nothing seemed to dry anyway
!), and absolute horror to wear on hot days. Not to mention it must suck to pack them (I've only tried them, never needed to travel with them). Neo suits might be a little more flexible but when you get the right size shell suit there is no comparison there.
And get a custom cut. From your name and little feet I assume you are a woman. I had the same issue with feet when buying. When I got to my size the feet were huge, and that is nasty because air would migrate there and be an issue (although sometimes one would be able to just change the socks/boots for little $). However, as a woman - unless getting women's sizing - you will find that there will be other issues too. Custom cuts rock, just make sure you get someone who knows how to measure.
I don't know which suits are pricy there but coming from Europe I would recommend looking into Santi suits. I have DUI and would get another one. Several other companies make good suits.
Other features to look for are robust boots, front zip, suspenders, pockets - some of which can be added.