I used a Helly Henson one at work once. That was very warm, have that with a normal jersey ontop and you will be warm enough(well i would, but then i was out today in 2 short sleeve jerseys and felt warm enough)
They are £27 if i remember right and they are pretty good.
Or there are Crag Hopper Merino wool ones thats £30something, never tried one of them on, but they look good and quiet a few people seem to buy them.