For the initial approval panel I wore trousers and a top. For the matching panel I wore smart jeans, cardigan and boots. I had put on a smart dress tried on lots of outfits but felt uncomfortable. I honestly don't think they even looked at what I was wearing
I went in 'smart-ish but comfortable'. Which ended up being nice colourful jumper with black trousers. Wear something comfortable is my advice.
The panel won't really care what you wear (assuming you aren't going to turn up in a Gaga meat dress and a mankini. Or au naturelle with a flourish and a 'we did mention our naturist beliefs at some point in homstudy, didn't we?')
Just look nice and presentable. You aren't proposing to wear anything which would make them think 'golly, is she really suitable to be a parent' so just wear what you like