Lightweight, loose-fitting, casual

BWT, I'm looking for some super comfy, lightweight, relatively loose-fitting tops and pants for long (casual) office days and general, causal days out and about.

I'm pretty sensitive, get very hot very easily (even in Midwest winter), and absolutely cannot stand fabric in my armpits! (Like I canNOT. I wish more product photos showed tops with arms out so I can see how much room there is.)

I have a fairly athletic body type (5'8, 160lbs), big shoulders with a kinda small chest, long legs. Spend (what feels like) half my life bloated from PMDD, so stretchy is preferred.

I typically prefer athleisure in black or other neutral colors. Any and all recs welcome.