Depends what style of alt you lean towards. What I do is I have a couple pairs of office trousers/pants that I like that I can pair with my Doc boots, other fun shoes, and/or office-appropriate alt tops. I am also a big cardigan girl, so I have a few that are neutral toned so it's easy to match them with various different tops all while keeping my fits appropriate. If you're not into cardigans, then the same applies to vests and button ups as well. If you have maxi/midi skirts, depending on their styles, you could potentially wear those too.
As for jewelry, you can still layer and have fun, but keep it minimal and modest. 3 necklaces max. As for rings and bracelets, depends on what you do for work. Less jewelry overall if your work is more physical. You don't want to spend your work day worrying about your jewelry and outfit alongside your work, it gets overstimulating (for me at least).
Hope this helps! <3