Welcome, Hedwig!
I recently searched for a black bag that would be dressy enough to wear with business clothes (suits, dresses, dress shirts, cashmere sweaters, dress pants, pencil skirts), but would also look great with jeans and any kind of top or sweater.
I ended up with the Black Crash TME Midi and it is exactly what I wanted. Although it is a black bag, it is not boring at all because of the black crash leather and the details in the design (drawstring, front pocket, rolled handles, bright lining, etc...). The clothes I wear tend to be more classic than trendy, so I love the way this bag adds some spark to my outfits.
If you need to carry a lot of stuff to work, the TME Midi won't be big enough. I use it just for my personal stuff since I always need to carry another work bag for my laptop and work papers.
Good luck finding the right bag!