Minecraft "non-violent" alternatives to get resources?

You can fish for it. There are small chances to catch some Leather as "Junk". Alternatively, leave the house's surroundings and get hunting some wild Cows / Rabbits / Horses.

According to this page from the official Minecraft Wiki, leather is typically only gained from killing Cows, Mooshrooms, Horses, and Llamas. However, a less reliable way to get Leather is to go fishing. Leather has a chance to turn up as a junk item from fishing, although it's much less reliable.

The only other option may be to find a Leatherworker villager, which will be wearing a white apron. The Wiki does not mention if you can buy leather from them, however you can sell Leather to the Leatherworker. Again, this is a much less reliable method, as you will need piles of emeralds to get the amounts you desire.