Can I do the DLC later?

I’m gonna be buying Elden ring with the DLC in 2 days, im quite confused as how the DLC works cus u need to kill mohg to start it. I just wanna complete Elden ring (base game) first then move onto the DLC but i also wanna kill every boss, so if i kill Mohg will it whisk me away into the DLC? Or should i leave for last? I wanna do the game step by step not skipping the bosses.