My advice would be wear whatever makes you feel comfortable and is non restrictive to physical movements. What works for me is a loose fitting T-shirt, loose and lightweight jogging bottoms, and a pair of light shoes with flat, soft soles (Feiyue kung fu shoes are my favourites). It is helpful if you can feel the ground through the shoes. Now you have seen what everyone else wears in the class you can structure an outfit that helps you blend in.
All the best