Does your Isotta wheel use a standard Momo/Sparco style horn button? Because of the center crash pad I wonder how well you 'll be able to integrate any aftermarket horn button. Is there any particular color, style, or motiff you're looking for?
I'm still concerned that any aftermarket horn button might have fitment problems due to the crash pad. Also, the trim ring is integrated into the crash pad so whatever you change to will clash. You could try any standard horn button from Momo, Sparco, OMP, or Grant. Alternatively, since you're a fan of the wood, you could see if the Knobmeister would be willing to make a horn button or a cover for your existing horn button that matches the wood on the rim.