There are few types of yarn that are available in market. Most suppliers only stock certain quality of wool yarn.
Most common wool blends are 100% wool and it blends with nylon or acrylic.
The softness of these wool are usually varies from 28 micron and above. Which is a usually considered coarse yarn.
Most common thickness of yarn is from 1/2 Nm to 1/2.5 Nm. Though thickness of yarn can be customized if ordered in bulk.
Some suppliers sells soft Merino yarn.