Do you have something like nice slacks that aren't black (lol, slacks, I think that's the word I mean)? You know, like tailored looking pants, but not as formal as black formal pants. I will see if I can find what I mean...

...okay don't Google Images 'slacks' just lots of daggy men and 90's office wear. I searched for women's tailored pants.
These are sort of grey? Or maybe black.
Sort of stone coloured. Obviously no thongs though!
These blue ones are cute.

So yeah, that sort of thing with a plain white or black tshirt, or an actual shirt.

You probably could go jeans, but as Jen says, better safe than spending the interview wondering if the jeans were a bad idea.

ETA: I reckon he could get away with jeans and a shirt, but with nice shoes. Sort of makes him look like someone who'd go fix the back fence.