This legit works.
Notes I took.
It’s not too complicated. It’s more work to have three spell types since the core book works with Int spells and Wis spells and don’t split them the way I see it.
Tweaks I’m trying this next session
A character can only carry one Yogstone at a time (10 mana for Int spells) and it takes an hour to attune to the Yogstone.
I don’t reward heart stones, because I like keeping players at 10 hearts. If you did, Charisma magic (spells that cost an HP) might be overpowered because it would give the character so many spells they could cast. If this was an issue I had to deal with I might tryout a rule that a character only be cast a Cha spell if the player has HP in their highest Heart.
Wisdom spellcasters can recoup a Wis spell at any time, but if they are in an unsafe place or spending an hour for the “ritual”, they roll at disadvantage. I don’t use 5e’s advantage/disadvantage mechanism typically, but I want that increased chance of rolling a natural 1 for rushing the ritual.