I have the opposite problem. My back seats are softer than my front seats. I read on another forum that Leatherique
(www.leatherique.com) was the way to go to make old, hard leather soft and supple again. So, I bought a bottle of the Leatherique "Rejuvenator Oil" and also the "Prestine Clean" leather cleaner. Used them four times, following the instructions to the letter. It made absolutely NO DIFFERENCE to the feel of the leather. It still has a cardboard feel to it and is just as hard as it was before I started the treatments. Maybe my front seats are just too far gone for anything to work, but according to what I read on the Leatherique website, the old, hard leather on my seats is just what their products were designed to restore. And failing them being able to completely restore the leather, I was hoping I might at least see or feel a small improvement but unfortunately, the only difference was that after the treatments my seats had, for days, the unpleasant smell of the Leatherique products, which is something akin to rancid cooking oil!!
So, I'm sorry I can't recommend a product for you as I am still searching for the same thing myself!
I totally had a feeling that those Leatherique products wouldnt work! This is so discouraging. Lexol was supposed to make them softer, but it just made the seats more shiny. Some have told me about sanding my seats and then repainting them for a softer finish, but that seems like overkill for good-looking seats.