Might be the obvious thing to do to make this one a gas giant, but it's a fun idea to work with. I admit it probably doesn't work with life as we know it on earth, but trying to come up with an ecosystem that has no ground to touch down on is something I've wanted to try for ages. I imagine there's even some difference in things living on upper layers where the atmosphere is somewhat like a terrestrial planet and then further down when things are starting to compress, so creatures in the depths have a little more buoyancy to work with but less light.