I've gotten to where I will wear long sleeve hooded t-shirts regardless of how hot it is outside (Columbia PFG and similar). They've gotten that material dialed in over the years to where the long sleeves don't make you any warmer than short sleeves, even if it is 100 degrees outside, but it does keep you warmer inside of a cold building (I also have the cold office issue so it works well for that too). There's a sweet one that Volunteer Traditions sells that I bought the other day. Of course if you're outside for long periods and pale like me despite going outside regularly, it has the added benefit of keeping the sun off of you.