Break up the familiar office combination
If you always wear the trousers with the same blouse, replace only that top first. A loose cotton T-shirt or more textured jumper changes the surface while keeping the familiar trousers. Choose something you already enjoy rather than searching for a supposedly casual piece.
Check the hem with other shoes. Trousers shortened for a higher sole may drag with flats. Another top alone cannot make them more useful for everyday wear. If you want several shoe options, the actual length needs to suit them.
Compare dark with dark
A black top need not match the exact shade of the trousers. Different fabric surfaces can make the separation deliberate. Look at the combination in the light where you will wear it, however. Faded cotton beside deep black smooth fabric may differ more than expected.
If you dislike that difference, put a clearly different colour between or over the areas. A pale shirt or coloured cardigan is easier than searching for an apparently identical shade. The existing trousers remain the base.
Use them differently on free days
Black trousers with a striped T-shirt and a short jacket can work for a walk through town. A soft jumper creates another, quieter combination. Try both with the same bag so you can see whether any further pieces really need changing.
The waistband should remain comfortable outside the office too. If you can tolerate the trousers for only an hour, they are not a dependable base for a whole free day. Choose another cut or investigate whether an alteration would help. More use comes from suitable wearing situations, not from forcing an uncomfortable garment into as many plans as possible.
