One of the simplest mods called Just Another Rotten Flesh to Leather will allow you to turn flesh into leather using a furnace. This is actually a convenient way to get the skin.
Just Another Rotten Flesh to Leather Mod for Minecraft 1.16.5/1.15.2
When killing zombies, now you should definitely collect flesh, because with its help you will be able to create a cleather for yourself. In order to get leather, you need to melt the flesh and thus you get leather at the exit.
Using the resulting leather, you can create the items you need. It is not always realistic to find a cow in your world, but zombies spawn every night and with him flesh always falls out of which you can now find an excellent use. In hard mod you will need to use four flesh to create leather for yourself and start using it in crafting.