I'm built like a scarecrow and as a result struggle to find baselayers that are snug enough yet long enough. I recently snagged the Merino 365 OG Long Sleeve with Thumbloops Top in a Medium Tall and couldn't be happier. It's the perfect weight, warm enough to keep skinny bones free from chills, but light enough to wear inside with the heat on (a conundrum in the cold months, freezing outside, sweating inside.) Sturdy thumbloops, reasonably sized crew neck. My only lament is that I am in the US and had to order from the NZ store and have it shipped from faraway lands instead of getting it closer to home due to stock, and the lament was neither the shipping speed (blazingly fast) nor the cost (offset by discounts and sales) but the carbon impact of shipping two shirts so far. Such is this life. It's a killer layer, I've already bragged to my entire scarecrow family that the fit is second to none.