Harvest & Mill
One of the cleanest American options: organic, often USA-grown cotton, milled and sewn stateside, real traceability, and none of the synthetic-fashion positioning. Reach for the undyed and naturally colored basics first.
Verify prints and any colored pieces before you buy.
A US source in the The Second Skin directory. Check that it ships to Europe; where it does not, the directory lists a European alternative alongside it.