For a coastal beach theme you can really have fun with the decor. Go all out with sea-inspired wall art pieces of coral and shades of blue and other soft/neutral colors. Pottery Barn even has these lovely sheets to go along with your beach look.
If you believe that green does not work in a trendy and minimal contemporary bedroom then think again! A green accent wall is easy to shape and it brings that much needed warmth to an otherwise cool and mundane interior.
Adding a similar unique headboard in your own home is pretty easy if you can find one of these antique doors and by just removing the existing layers of paint and painting it white you get a headboard that is both refined and shabby chic.
You can also have some real fun with the bedding. BHG shows a couple of twin beds with cute designs on the sheets plus trees and owls on the decorative pillows. Or why not keep it simple in the country? These two beds feature crips white bedding from Crate & Barrel with a bright green wall behind them.