Kebab's Armor Overhaul
Greatly improves all armor textures, while still making them feel like vanilla textures.
I will consider doing the turtle helmet as well.
Optifine is not required for this pack.
Check the FAQ at the bottom of the page for permissions.
Screenshots
FAQ
Can I use this in a modpack? | Yes
Can I use some of these textures for my own (public) resource pack? | No
Can I use this pack on a server? | Yes
Can I redistribute this pack on another website? | No
Does this pack work for X version? | I think it should work for most versions of Minecraft (at least 1.12+)