First of all, do you like the sea grass? If so, a simple fix would be to build out the size by adding wood. Mimic the shape of the existing headboard, only larger in wood. Another option is to add a backer of plywood, enlarge to full size- you can do any shape- cover in batting and a fabric. You may have to attach the headboard to the wall. http://www.thisthatandlife.com/2012/07/diy-upholstered-headboard-tips/ Most lumber yards will cut wood for you. The link here is a DIY step by step.

paint a full sz headboard behind the twin if the room is blue and white, paint the wall headboard white.
you can follow the shape of the headboard or get more creative with tall look with beige or silver swirls.
to go one step futher : buy or make a simple crown. hang it high on the wall and use an abundance of white mosquito netting pulled to each side and falling to the floor.