I only use italics if the thoughts slip into first person or second person when I am writing third person.
If I am writing first then if my character is thinking in third or second then I use italics.
EG @tinkerdan I am tired so I am nicking John and Mary. If I ever get any royalties from them I will share them
Mary trudged after John, her feet were aching and her stomach was so empty it was making so much noise it reminded her of entire section of an orchestra. There was still no sign of the restaurant. She stuck her tongue out behind his back because he was setting the pace she couldn't keep up with. If we pass that Italian one more time, I am going in, I don't care what he has planned. The smell is making my stomach ache.