Single, larger blossom flowers, such as roses, carnations, zinnias, tulips or lilies, usually make up the focal points of a piece. Taller stems with multiple flowers can balance things nicely. Delphinium, gladiolus, and snapdragon are good examples of flowers that can add extra height and texture. "Filler" flowers, or stems with many small buds, are great for topping of a bouquet with a full and delicate look.
Whichever way you decide to go with your flowers, a lovely idea is to try and tie your whole theme together so if you're going for roses, then have a rose design featured somewhere within your headdress. Look out for a company who can work with you and your designs and most importantly your budget to create that one_off, bespoke creation just for you.