With wrist supports, DIY is the way to go. I made one for my wife when she needed one a few years ago - moulded fibreglass directly on her wrist (with clingfilm and a piece of t-shirt fabric in between). The stuff gets very hot while setting, so don't make it too thick - make a thin layer to get the shape, then trim it and add an extra layer if necessary. This was far more effective and comfortable than an off-the-shelf one.