We went for curtains from Deliah's Camper furnishings.
They are a bit pricey but the quality is superb (which you would expect from a professional).
We then sewed some small neodymium magnets (about the size of a 5 pence piece but very strong) into the top and bottom hem of the curtains and they just stick to the metal body of the van, no need for curtain rails and drilled holes etc. We just slide them back when not in use and they stay stuck to the van body, or you can remove them all together when not in use, very versatile.