I find that my Merino t-shirts itch just a bit until I get a sweat going. Dry skin I suppose.

I like a lightweight T shirt under a mid-weight long-sleeve, or 1/4 zip for layering,
Change out the T-shirt & boxers after a day or two.

With daily sponge baths etc. of course.

For higher intensity sweat intensive activities like XC skiing, I still prefer layering synthetic grid fleece of appropriate weights for the temperatures encountered.

But nothing beats the comfort of Merino.

History May Not Repeat, But it Rhymes.