I would suggest earth tones like brown, darker greens, ect... These will look nice but, if you pick the right shades, should not overly compete with the orange curtains.
What color of sofa and carpet will match white walls and orange curtains?
Hard to find, but try: An light olive sofa or two of them with dark magenta pillows. Grays and Black & White zebra if you need lots of pillows. It is vey in BTW to have nothing match, pillow-wise. Those orange curtains lead up to humor, so decorate non-seriously.
Wicker furiture could Work well, too.