The larp does not aim for complete historical accuracy, but an overall look that is close to the fashion of the 1910s. Since you will be playing together in your bedrooms, you are also expected to have underwear appropriate for the larp.
To help and inspire you, there is a Costume guide and a Pinterest board.
Later on, there will also be a costume group on Facebook, where you can ask questions, share tips and buy, sell or borrow from each other.