Iain Smith who I've just done my Cave course with had a Santi 200gm made to measure under suit which was a lot less bulky than a 400gm and would make a really toasty combination with a set of Arctics. MTM for not a lot more than a hundred quid. I think most of the trick is keeping head hands and feet warm as well. I have a 5/7mm Waterproof hood, Xerotherm hotsocks as well as artic booties and dry gloves. Works wonders. You carry a lot less bioprene than me Adam
- might mean you're always colder and need a bit more in the way of baselayers. I swear by drygloves in the winter - they make a huge difference. HTH