I am writing a fantasy novella that ends up using a lot of internal monologues, often mixed with dialogue, descriptions, and other character's monologues. For example, this excerpt from the first chapter
Yoshida’s head was aching from where he had been hit. A bright light shone in his eyes, and he clenched them tighter. A cool, damp breeze wafted across his face.
The long blades of wild grass rustled as Yoshida sat up, his eyes flying open. A realization dawned on him as he looked at his surroundings.
“A forest? Wasn’t I just in my office in Tokyo?”
Dumbfounded, he sat for a moment. The forest seemed all too familiar, with its Japanese beech trees and ferns.
(It reminds me of when I visited Shirakami-Sanchi, that forest up North) he thought to himself.
He looked down at what he was wearing, and saw black cloth, brown leather belts, and chain mail peeking out from under a jerkin.
(Wait a minute, is this my Guild Mythos character?)
Day to day, Yoshida acted as the head of a small game-testing firm. Having been unsure of himself during his school days, he had taken journalism and game design courses, eventually making a name for himself as someone with a keen eye for quality Massive Multiplayer Online Role Playing Games—MMORPGs.
I chose to use parenthesis to be a clear indication for when a character is thinking for a few reasons: Firstly, I originally wrote a lot of the dialogue and internal monologue as new lines. Secondly, I wanted a very clear indication of when a character was thinking. Thirdly, I simply didn't know that italics were a standard.
The reason I wonder if I should change it is that I have written the entire book in this style. While I'm not opposed to changing it, I find that the parenthesis work well for what I use them for, and don't obfuscate what I'm trying to convey. Since I have used them throughout the entire novella, would you recommend leaving the parenthesis, or changing over to italics?
As a comment, I haven't tried italics yet, but I think they would make the internal monologue a bit harder to differentiate from the normal text, which the only other reason (apart from reducing extra work) I wouldn't want to make the change.