Is a midweight wool layer, perhaps worn over a T-shirt, warm enough? If so, Smartwool makes a long sleeve, midweight crew:

http://www.moosejaw.com/moosejaw/shop/pr...08_10000001_-1_

I wear Smartwool microweight (lightweight?) T shirt under the half-zip version of the above, and it's warm while hiking down to about 40 or 45 degrees (depends on wind.)