Depends on your place's dress code. If you're new to the place I'd observe how others dress to get a general idea of what's OK to show up in and what isn't.
Our place is very relaxed and you can wear tracksuits if you want to, at least once you have the job. You're expected to dress quite smart for the assessment/interview process (at least most interviewees do because they want to impress) but once the job is yours you can dress down quite a bit, depending on which department you're with (ours is probably the most relaxed one). I'd probably dress fairly smart to begin with and then relax as time went on. I'd say our management would only say "okay, this is too much" if people started showing up in onesies and even then I'm not so sure, haha.
We can also wear whatever shoes we like, but if they're funny about shoes you can easily get a nice comfy pair of black plimsolls to change into once you're there, they're cheap as chips. I have some as well as a change of socks just in case we get a crazy amount of snow and my feet get wet on my way there. Nothing worse than wet feet!