The song is good. The instrument choice is limited by what you play, I'm guessing.
The intro would probably work better as an instrumental bridge, right after the "Don't go acting like you don't know" lines. Then you can drop it all out, for the cool dynamic effect you seek.
I'm liking the lyric a lot, & the piano should be more pronounced, esp in the chorus. Little twinkly tinkles on the keys throughout the verse would be nice, too.
The intro line, being used as a bridge, could be played on a bass, with the other instruments falling into place as it builds. Just thinking off the top of my pointy headbone.
It needs some serious arrangement work, & yeah, your voice may be a little weak, but it works for this piece. You're writing for your own voice, which is a wunnerful thing to do. To balance it out, you could have some b/u voices echoing your lines, like, a beat behind your own. That would fill it out, & emphasize the lyric.
I can hear this, in my mind's ear, starting off very simple, but building & building throughout until it's almost a big production piece, then, at the outro, returning to the very simple, in the slower tempo.
It could be beautiful, overcast. Well done!
SMILE - it's the safest way to spread your cheeks!