There is no problem in left foot braking, ONLY if you have mastered the technique. You must leave the accelerator, when the brake is engaged with the left foot. There is nothing wrong with it if you are okay in stopping the vehicle progressively.
However, since yours is an automatic, I would suggest driving lessons during early morning on empty stretches to practice right foot braking. This way, you will get a feel of it and soon it may become your habit. Saying this only because, you might come in a situation where you have to drive a manual car, then you would be having the habit of pressing lightly with the left foot (earlier brake, but that won't work for clutch) and the right foot would have the habit to stay on the accelerator (whereas in manual you would have to move between brake and accelerator). Trying heel and toe technique is useful in using left foot braking in manuals, but I would NEVER recommend it. I almost had a crash while learning that technique. Dropped the idea then only!