Cat off the leather sofa

I am about to buy a new leather sofa and I don't want my cat to ruin
it by scratching it to pieces. I know that they sell some sprays for
this purpose. The problem is that I live in a studio apartment.
I do not want something that is so strong that my cat will be
uncomfortable in the apartment. I just want to keep him off a
particular piece of furniture. Can anyone recommend a product that is
effective, but not overly strong. Thank you