You probably aren’t going to make appreciable gains from going from sonic barrier versus denim. If you are unhappy with your results, you always can make that jump later.
You can lightly stuff some acousta stuff if you want. Just add a little by ear. I would listen to it first, then if you feel you need it add some.
I would probably just leave the bottom as is. I don’t think you will really be able to get it off later. You can always stick some foam down there to help with reflections.