I certainly don't eschew non-vintage fabrics such as fleece, though I do tend to prefer the overall aesthetics of vintage styles. The C-2 is something I really, really enjoy wearing, largely because it fully zips and is easily removed and put on, and it fits so snugly without bulk as a layer under snug-fitting jackets such as the A-2 or my new-found love in the ELMC Californian jacket; the fact that the C-2 is period-correct is a bonus. My C-2 is also an original, but I have a Buzz Rickson's in navy and in black for other color combinations. Fleece may well be superior to the C-2, and if I could find one that hugs my body as well as the C-2 and has a full zip, I'd give it a go. Any thoughts?
I have fit images to post of the Buzz Rickson's Rough Wear B-10, which I hope to do this week, then you can compare this version to the top-selling Superior Togs.
Charles, in terms of a nice vintage-style/traditional fabric undergarment, have you looked at the Filson mackinaw vest? They come in different colors and fabrics (wool, moleskin, etc) and are numerically sized (40, 42, 44, etc) for a snug fit under a jacket. I have a charcoal gray 24 oz. wool mackinaw that is absolutely perfect for layering under a waist-length jacket. Very warm, functional and stylish too.