A lot of leather noise comes from or in between the top and bottom seats, i.e. between the back rest and bottom. It is pointless applying the leather 'food' on the seats only hoping to reduce the annoying noise when you are not tackling the root cause of the problem.
As a restorer, we will generally apply lots of leather cream or conditioner in between the seats and allow it to soak for a while, you may wish to apply once more. You will be amazed at the tremenduous reduction in leather rubbing noises in the cabin ... but total elimination is almost impossible unless you use fabric or PU interior.
Good thing is genuine leather tends to make noise ... so be proud knowing that the leather in your car is genuine and of good quality.