Waitrose do a
natural 'dry powder' carpet cleaner - but it works wonderfully on velour type upholstery. You just sprinkle, brush it in with the brush provided (not very good) or a nailbrush, washing up brush, or similar (not too rough bristles), leave it, and then hoover off. It really does brighten things up and smells nice too. Best of all, it doesn't leave the cushions damp at all so you can do the job, and not worry about the cushions drying out. It comes in a pouch, which is resealable, and it really does work!
I'm sure you can buy it elsewhere but I've only seen it in Waitrose - though I've just had a look and Amazon are doing it -
Natural and Clean Carpet Cleaner - I think it actually cost me less in Waitrose!!!! There are lots of other powder-type products, but I like this one because it doesn't contain any nasties. It also nicely lifts and cleans any marks on your carpet.
If it's a woven cotton-type fabric, rather than a velour, then you may need to use something else.