The Mantle has great protection but you can improve it by attuning it. Unfortunately you can’t use the Attunement Altar. Instead you have to use the Iridescent Altar (the one you crafted the Mantle in). Pick a Constellation you wish to attune the Mantle to. I would suggest you choose the same Constellation that you bound YOURSELF to.
In the Tome, look for that Constellation (under the Constellations Tab) and scroll to the end. This will tell you what ingredients you need in the Iridescent Altar and in the Relays once you start crafting.
It's also VERY important you insert a Celestial ATTUNED Crystal into the Table on the left:
These Mantles are VERY enchantable and can be done with either the Refraction Table or via the vanilla methods (books in an anvil, etc.).