I didn't expect to want to wear this everyday all day, but I do. It's lightweight and can be either warm or cool as I need it to be- the magic of merino! About sizing- I first ordered mediums (in tank, undies and tights) based on the size charts- I'm typically an athletic size 6 at 5'5" but not busty. 34.5-29.5-38. And exchanged them all (very easily, thank you!) for smalls. There is ample stretch in the tank. (Undies and tights too) The tank is body hugging, but not tight. My first experience with this company was wonderful- from the ordering to the packaging, to exchanging, and product fit, quality and comfort.