First of all, we get Axolotl with a bucket.
Then we get a Leather Helmet.
Now, we combine these items on the Blacksmith's Table and make an Axolotl Helmet.
With the Axolotl Helmet on our head, we have the Regeneration effect. We're also immune to the Mining Fatigue effect.
and finally, we can repair this item in the anvil with an Bucket of Axolotl without the need for a new a Leather Helmet.