Leather Sofa Conditioner Recommendations?

I bought a couple of leather sofas (from SCS) about a year ago. I don't know what type of leather it is, but the finish is dark brown, with the surface texture not completely smooth - it has a network of little lines all over it, much like the skin on the back of my hand when I look at it closely.
They still look like new but I'm told that they wont stay that way unless I look after them. This apparently includes applying some sort of cream or conditioner, maybe twice a year.
Can anybody recommend a product for this job, or offer any other hints?

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