Cant edit the game now sadly, just your title and stuff but not the game.
But if you still wanna edit the game after for yourself or something yeah adding some sound effect like for the jump and stuff that would really add an extra level of feedback for the player.
Plenty of free resources online like I use "Mixit" personally, also plenty of just royalty free SFX on unity asset store or YouTube.
But other wise great work, this could be a really nice little portfolio piece the artistic style really sells the game.