Wool

Wool is a renewable source of fiber every year, sheep who are raised on open range and rotated regularly can be regenerative to the land.
Wool fibers can be bent back on itself more than 20,000 times without breaking, and it's flame resistant with a ridiculously high ignition point of 570 - 600°C/ 1,058 - 1,122°F.
When it goes back to the land, wool breaks down slowly. It's made of about 17% nitrogen and releases nutrients into the soil as it degrades, and only takes about 6 months in the ground to go back to the earth.