We always advocated natural fibres in the mountains years ago but the development of efficient thermal base layers has virtually rendered them redundant. We also used to wear tights as a lower body base layer and these were incredibly efficient. Not sure which denier.
In the winter mountains, my usual is Helly Hansen base layers which are totally efficient and non constricting. On top of this, I wear Buffalo gear which is Pertex breathable outer and a fleecy inner. Nothing else needed down to about minus 20. The main difference, of course, is that one is normally on the move, which helps to keep the vital juices flowing to the outer limits. This is not an option on a small boat, unless someone can come up with some calisthenic exercises whilst tackling a large cod (I should be so lucky). Rich is quite correct when he says that if you are feeling cold, the first move should be to don a warm hat. The secret is not trying to generate heat within the body, this can only be done through food, but to preserve what you have got. This is why those awful silver thermal blankets are only of use to stop the loss of body heat. Put them on somebody who is already cold and they will stay that way!
Sorry to go on, but this subject is one of my special interests when training mountain leaders. When working out your warmth producing tactics for the day's fishing, don't forget your choice of food; this is what produces the inner warmth. But that's another topic.