My 'go to' sports bra is a Champion compression bra that I normally use for all my fitness activities (I have 5) however just yesterday I realized that I packed a pair of compression running shorts instead of my bra! I figured if I could garden all day in this bra, I could certainly do yoga. I did a fairly tough 90 minute flow class followed by a 1 hr restorative and was just fine. I usually wear a loose sweater (washable wool) over a tank top that is snug at the bottom (stays in place during inversions) and bra and remove the sweater when I get warm. Restorative requires layering up again and we even use blankies, so I put the sweater on and wool socks.
Folks wear everything from standard gym shorts and cotton tees to Lycra combos. (Classes are co-Ed and well attended by guys of all ages). One teacher (male) wears t-shirts with yoga motifs and white cotton trousers that look like the bottom of a gi. Another teacher always wears a dropped crotch pant and cotton top with long sleeves. The other two I know wear black Lycra capris and loose tops with some arm coverage.
My yoga classes are at a YMCA, so no fancy stuff like hot yoga, which might require a different kind of outfit.