You can fight that boss at several different points of the play through depending on certain variables. Tough to say.
I believe there are 19 bosses including a couple optional and hidden bosses.
So could be 7 or 8 left including some optionals. Or 5-6 if you don't do optional bosses. Or maybe even 8-9 if you didn't fight any previous optional bosses.
I think there is 13 bosses you HAVE to fight, 6 you can but don't have to.
I beat the 3 lords of cinder and was teleported to the dancer fight, am I almost done the game, cause I dont wanna rush through and pace myself if there's only 1-2 bosses left.