I’ve used both Chamberlains leather milk and Obenauf’s Leather Oil. The Obenaufs is more for restoration and the leather milk is better for maintenance. Both are affordable on Amazon.
This is pretty close, better than what they used in the Middle Ages for leather
https://www.amazon.com/Obenaufs-Leather-Condition-Restore-Applicator/dp/B003EAW57E?