I second the Academy "Magellan" brand as a great, inexpensive way to augment your system. Also second the neck gaiter - I use a thin merino one by Firstlight and a second fleece "TurtleFur" one. By far my favorite mid-layer is a pair of 3/4 length zip off Kuiu pants (I think they are in the Peloton line). Super lightweight and awesome insulation; and you can get them off without getting naked.