Bit of an embarrassing question really, in that the answer is probably obvious.. I've got an Otter Polar D two piece thermal suit, that I wear under my dry suit. Its great, but I'm sure the weather is going to get colder soon. Now I've heard and read various people talk about adding layers when the weather takes a turn for the worse. What kind of considerations do I need if I want to add another layer to the Polar D? I appreciate additional weight will need adding to me and a weight check doing again. Presumably I would wear something underneath the Polar D or would that be ontop? Choices I have heard mentioned when people speak about layering include - Merino Wool - PolarTec Any pitfalls to avoid?