thee is correct for the objective form of the informal second person, while thou is corrective in the subjective/nominal case (as the first part) :
I, thou, you, him, her, us, ye, they - subjective
me, thee, you, he, she, we, you, them - objective
my, thy, your, his, her, our, their - genitive
mine, thine, yours, his, hers, ours, yours - possessive
slang can work but you may want to keep it more consistent. For instance, "is" came into fashion for the third person after "thou" fell out of fashion : "There beeth" would be the working term. Ain't, as a contraction, is also modern, but am and not were both words of the time so it could slide. "Why" is also modern, in the past "wherefore" fulfilled the role of interrogative and "whereby" established cause. "Why" at the time was an invocation used to indicate an interrogative phrase and did not serve further grammatical purpose.
it is also a modern/informal thing to include qualifying phrases which affect the subject after the object, which cure alludes to intentionally or unintentionally in his moving of "yet," for what that's worth.