I was trying to homebrew the Celestial Tome of Healing from The Griffon's Saddlebag. In part it reads

This golden-paged tome has a diamond embedded in its cover, which emits a soft glow whenever the book is held. The following spells are written in the book using a strange form of Celestial that's only legible to the creature attuned to it: cure wounds, guiding bolt, healing word, and mass healing word. While attuned to the book, you know the sacred flame cantrip, and you can prepare the book's spells as if they were wizard spells whenever you finish a long rest. Whenever you expend a spell slot to cast one of these spells, you must expend a slot one level higher than the level at which you cast the spell.

It adds spells to the list of available spells to prepare, which is different from automatically having spells that are able to be cast. I'm not sure how to do that, or if its even possible for that matter. Adding to the difficulty is that the spells are cast with a slot one level higher than normal.

I suspect I could create a slightly modified homebrew wizard subclass with those spells available, but I'd rather have it part of the magic item. Second best option would be in a feat.

Not possible with either a magic item nor a feat.