Personally I prefer to fill the pot with soil. You want a consistent material texture all the way through the volume.

The alternative is to locate a product called Ups A Daisy planter inserts that effectively lift the bottom of the container and reduce the volume of soil needed. This is a far better and less messier solution than filling with the Styrofoam pellets, landscape fabric and soil.

Here is a link that might be useful: Ups A Daisy

Moving a heavy pot is unpleasant, but making a top-heavy pot can really break your heart if the wind knocks it over. I agree, I'd not use something that was like a different layer of 'dirt' to the roots. Something that takes up space with air will help keep the weight down. An empty nursery pot, upside-down in the bottom can give plants a lightweight lift, as well as empty plastic bottles, or other plastic containers.