soundprofing edm studio room
You're right that the sound blankets will do little if anything to soundproof the room. They mostly just serve to reduce echo.

Hanging MLV curtains on the walls will probably make a noticeable difference at higher frequencies, but won't do much to stop bass. You can get somewhat better results if the curtains are separated from the walls by a good distance (a few feet) but again it's still not going to do a lot to stop bass. You can add in a riser that isolates the sound from the floor, for a bigger improvement.

But your only truly effective option if you can't modify the existing construction is to build a room within a room, with its own isolated floor and ceiling.