When one is writing in the past tense**, it's easy to indicate thoughts by including sentences in the present tense, with or without italics, with or without a 'thought tag'. Starting with the straight narration, He watched the bird launch itself from the branch and wished he could fly.
He watched the bird launch itself from the branch. I wish I could fly.
He watched the bird launch itself from the branch. I wish I could fly, he thought.
He watched the bird launch itself from the branch. I wish I could fly.
Personally, I think the third of these doesn't seem to work as well, but that may be because I've been brought up on books that tended to italicise all thoughts. But it does have one advantage, which it shares with the version with the 'thought tag':
He watched the bird launch itself from the branch. I wish I could fly, he thought.
He watched the bird launch itself from the branch. I wish I could fly.
which is the ability to add emphasis. (One can, of course, do this:
He watched the bird launch itself from the branch. I wish I could fly.
but, to me, it never has quite the same impact.)
But to answer your specific question, you
can use both italics and 'thought tags', and mix them if you want, but if it stands out from the rest of the narration (and you don't necessarily want it to), you should stick to one method or the other (within the PoV***).
** - Of course, when the narration is in the present tense, you probably need to use the thought tag or italics (unless the narration is also in first person, when everything is thought, really, isn't it?), because you have no other way of identifying thoughts.
*** - Having different PoVs doing it in different ways is one way of reminding the reader whose PoV it is. (I think Joe Abercrombie does this.)