The more informal way to say that you will study a lot tomorrow is: "Voy a estudiar mucho mañana."
However, among the options given, none appear to be informal alternatives to the original sentence, as they all seem to maintain a formal tone or are incorrect in terms of grammar. The most casual and typical way in conversational Spanish would be:
- "Mañana estudiaré un montón." (Tomorrow, I'll study a ton.)
But from the options listed, "Voy a estudiar mucho mañana." is still the most informal way provided.