You can always buy it when the hair loss occurs. It's easier to match hair color and style with your present head of hair. Sometimes hats, scarves, or turbans are more comfortable for indoor use. Get a variety. If you have long hair, you might consider getting a shorter haircut to minimize the trauma of hair loss.
Shorter hair is easier to manage under a wig.
A shorter style will make your hair look thicker and fuller. It will also make your hair loss easier to manage if it occurs. Use mild shampoos and conditioner. Use soft hairbrushes. Use low heat when drying your hair.