I do not hate my job. Let me just start with that. In fact, I love my job. I made a big change a few months ago, and I do not regret it one bit. I have been interviewing for a few different companies because I just need something that provides a more steady income (I can work my current job part time if I wish), as well as develop better interviewing skills.
The most recent interview I went to was through a staffing agency, so they wanted it to be informal. This does not mean yoga pants and Uggs, people. This would be more business casual. I definite business casual as flats and no blazer. Even though it is informal, the agency wanted to see what kind of candidate they are bringing to their client. Of course they want to make sure that they are not bringing a complete slob to their client, so it is importantly to dress neatly.
Instead of a full suit and heels, I opted for a fitted blouse and dress pants (everything but the jacket, know what I mean?). Instead of heels, I went with some driving moccasins. For some reason, ballet flats with dress pants just are not a good look on me. I was also coming from work, so I did not want to over-dress for either groups of people.
Definitely look for a spiffier outfit for the formal interview!