Marseille Soap apparently can be used on leather. Has olive oil in it.
There are great unholy gobs of olive oil 'Castile' soaps on Etsy.
The soap doesn't matter as much as the tanning. We've known one basic fact since World War 1: veg tan leather falls apart when water is allowed to soak in. Which is why we invented chrome tanning.
Have you actually tried my carpet/upholstery foam on a nitrile glove trick? Foams -> minimal wetting, maximal defunk.
Muc-Off took the carpet foam idea and ran with it to make Foam Fresh. Carpet foam for sports.
Stay fresh out there!
us.muc-off.com
But they f*cked the fragrance part: way, way way stronger than it needs to be, headache inducing levels.