I would like to add the Herman Miller Aeron.
It can be expensive ($800) in ones and twos, but I love mine, and I’d happily pay it again. As far as the requirements goes, it checks:
Supports 300 lbs. - Chart here goes up to 300 lbs and 6’6" with the C chair size https://www.hermanmiller.com/content/dam/hermanmiller/documents/product_literature/other/ap_sizefitref_classic_aeron_chairs.pdf
Stain and odor resistant - The chair isn’t a hard plastic, so it loses some point here, but the mesh doesn’t hold smell, and any stains/grime can be washed out pretty easily.
Designed for high comfort in a work environment - Checked. It’s “the standard” that everyone compares others to.
Back support to reduce strain and fatigue - It’s customizeable to allow different types of supports for the unique body types of our members. This does have the downside of it allows customization and you might spend the first minute of sitting in the chair setting it up for your body type.
High durability with warranty - 12 year warranty.
Casters strongly preferred - Check. They have both carpet and hard surface rated casters available.
Cost effective (<$500/ea) - Biggest downfall of this chair. $750ish new, it blows the <$500 point, but I suggest we order a couple and see if they are well liked.