Italics
If I understand correctly, you are indicating spoken dialog by regular use of quotation marks. No problem.
Your problem is you want to use italics to indicate thoughts and dream sequences without confusing the two. I'm assuming italics are also being used to indicate titles of books, plays, ships, bridges, etc., as well as emphasized and foreign words.
I have a similar concern in that I indicate signed dialog (by and for the deaf) by italics.
To do so -- as well as indicate emphasis, titles, and foreign words -- without confusing readers, I opted for another kind of thoughts. I indicate them with direct (he thought, she thought) attributives and indirect attributives:
There's no way, he thought. I won't do everything her way.
She looked on in horror: This isn't happening to me!