I'd recommend Soft Paws.

My cats, Angel and Dillian, wear them. We bought new leather furniture a couple of months ago, but before we bought it, my family researched Soft Paws. We KNEW they would try to scratch the new couches, even though they have a scratching post, and I really recommend them; they work. It may be a battle to get/keep them on at first, but they get used to them, and it's pain free.

Here's their site if you're interested: http://www.softpaws.com/ .

Good Luck!