Can you get a picture and/or model number for the Eheim filter? If it's a classic it should have prefilter in the bottom, a blue coarse filter pad, biomedia, and then a fine filter pad.
I just bought a CF-400UV. I'm going to use substrat pro in it. I'm not sure how much you wanted to spend, because you would have more money in media than in the filter. Pot scrubbers and lava rock aren't that high in surface area, so I'd always recommend some type of ceramic media meant for...