Certainly dual rollers have a more contemporary look, especially when they are used with a sleek fascia. Dual rollers offer huge versatility in light control and have minimal upkeep (read- no dusting required :-) ). The big thing that is going to determine what you do is the amount of depth in your window as dual rollers require a fair amount of depth. I've attached a photo to give you a sense of depth though the requirements certainly vary with manufacturers .

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This made me laugh: http://www.theguardian.com/environment/2016/jun/09/seagull-turns-orange-after-falling-into-vat-of-chicken-tikka-masala I couldn't copy the picture, but it's hilarious.

You are correct the place does and always will look a bit sparse when you only have blinds. The question with curtains is sometimes dependant on what climate you live in and I am not sure where you are so I am going to say. If you need curtains for heat go for a quality curtain to the floor with a fabric that is not stiff (as I discovered I now own after buying curtains off line for my spare rooms). The expensive curtains I brought for my living room have a softer texture and hang so much nicer. As I need Curtains / Roman blinds for heat I have backing fabric etc on the expensive made to measure ones, where as the cheaper ones are just thermals. If you only want to add a curtain for looks and do not require it for heat I would recommend going with a lovely sheer / half see through fabric that drapes really well, this will add a point of interest and you can colour match or add a loved colour to a bare - white on white - cream on cream - colour scheme.