Hi Jjsloane --
Congrats on the new job! I know the vibe. Two words: cashmere hoodie.
Lots of great ideas above.
Q: Are you a fairly formal person in terms of manner? I'm not, so I think that helps. I just say things like, "don't be alarmed, I'm wearing a dress PLUS A PRINT today but don't worry, I'm not handing out a pop quiz." I've turned up in similar items to the (much younger) staff, just styled differently, so that gives commonality.
I'm also not super-polished and have to actually pay attention to that at some sites / for client meetings! So if you can dial back on perfectly done whatever without feeling scandalized that can help balance out the dressier clothes. [Some can't do one without the other, I know.] Or have "done" nails but in flashy, on-trend colors.
IDK...I'm not an sporty, natural/rustic, or unisex dresser so I just stick to my style but make sure to incorporate elements that would be wildly inappropriate in a formal business environment. Really the more the better.
Trying to think of warm-weather examples that I've worn or have ready to go in case it ever GETS warm.... Really just echoing above but color, print, bold are inherently more casual.
-- metallic sandals + dangly earrings + silk whatever in bold print + "office-y" pants/skirt/dress
-- knee-length linen cardigan + column of color (denim flares + dark blue top OR jersey dress ]OR print jersey skirt and top)
-- longer (mid-thigh to knee) tunics over flares or skinnies or "office-y" skirts/dresses
-- print bomber jacket (or hoodie if you can!) over jersey or more "office-y" skirt/dresses
-- not as much my thing but pattern-mixing