At work today, we did an ice breaker with a picture of 9 cats which we had to choose from to express how we were feeling. There was one cat w/ a sombrero which prompted me to answer in Spanish that I was that cat today. I struggled to decide whether to use "soy" or "estoy" and opted for the latter since I was expressing my current state today. However, "soy" feels much better and I think that could be the preferred way to express that sentiment. That is, at least, if I'm going to try to express it with the verbs of "being".
Perhaps it would be better expressed, and would be by a native speaker, in a way that'd translate more literally to "I feel like ..." (ie. "Me siento como ..." or "Estoy como ..."). Certainly, if you were pretending to "be" someone else you might use "soy" as in the assertion "I'm Batman" but in the scenario above, I'm simply trying to express how I feel and comparing myself to one of the cats. Perhaps it's very "English language" to even express that sentiment as "I am" such a thing in the first place.