I wear my Woolx base layers everyday during the winter months. I can't say enough good things about the product. Everything you read about Woolx online by the vendor is true...it doesn't itch, just throw it in the washing machine, it regulates body temperature without overheating. It's the best. I am 5'7", weigh 124. I have two midweight shirts in small. I tried a medium at first, but it's really a bit too big for me. Then I ordered the leggings. I went with medium based on reviews, but I think small would have been fine. I ordered the vest in medium as well, and it fit nicely, though I thought the arm holes were small, but if you are only wearing a Woolx base layer underneath it works just fine. I really love the pockets in the vest too. All good products, so far I am a big fan!.