Your basic, useful, long-sleeved crewneck T, in a really lightweight wool that you can wear even on warm days, and it doesn't make you itch unless you're too sensitive  to begin with, and then all bets are off. Wear this long-sleever with one or two or even three other superlight wools, in sleeveless, short- or long-sleeve, and the combo will be warmer than a single thicker layer, and more versatile. More expensive too, but once you have a bunch of these they'll last for years, and if acquiring them doesn't cause fights at home,  it's a good way to go.

Here's a sizing chart.