[Help] What fabric to use for an Ace Attorney vest and help making buttons.

Hello all, this is my first time posting here, but I've made cosplays in the past. I'll be cosplaying Franziska von Karma from Ace Attorney and was wondering what kind of fabric you all would recommend for the vest. It looks like it's a suiting kind of material, so I don't want to use regular cotton, and I was recommended broadcloth but I worry that will be too thin.

Also, I need to make her diamond buttons for this. Should I sculpt them out of clay or is there an easier way to go about it?

Thanks for the help!