School of Tattoos

As a solution to the fragility and vulnerability of requiring your spellbook on you at all times, these wizards use their skin as a replacement for parchment, inscribing their spells onto themselves.

Skinbound Spellbook

You become proficient in Calligraphers Supplies (the closest tools to Tattooing that I could find), using them to draw tattoos of your known spells. When you pick this class, your spellbook is destroyed. Your tattoos can only be disabled by dismemberment - scars, illusions and tattooing/branding over them has no effect. It costs you the same gp in materials as normal to learn new spells, but twice as much time, to reflect the difference in skill required to tattoo yourself. Your skin also becomes able to act as an arcane focus while you are not wearing armour, allowing you to ignore the material costs of spells unless there is a specific cost in gp. Your number of spells known and prepared is not changed. If you find a spell scroll you can either add it to your permanent spellbook as a known spell or add it as a tattoo version of the scroll, costing 10gp and one hour to do either. Both options destroy the scroll. 

Enhanced Form

Inscribing spells on your skin has toughened it, and as a result you gain a number of extra attunement slots for magical tattoos equal to half your CON modifier (rounded up). You also gain advantage on Constitution saving throws.

Unarmoured Defence

Beginning at 6th level, when you aren't wearing armour or using a shield, your AC is equal to 10 + your INT modifier + your CON modifier

Arcane Intuition

Your physical connection to magic has granted you an unnatural sense for when magic is around. You learn the spells Detect Magic and Identify if you haven't already, and gain advantage on all saving throws against magic of any kind.

Temporary Tattoos

Beginning at 14th level, you gain the ability to create tattoos of spells on other creatures skin. As an action on a willing creature your are touching, you can cast a spell you know at the desired level, but instead of the spell being cast as normal, it becomes a temporary tattoo that the recipient can use to cast the spell later without expending spell slots. Once the tattoo spell is cast by its recipient, or after 24 hours, the tattoo disappears.