What you’re describing is called a ‘gravity couch’ and the concept has been around for a long time. While liquid isn’t compressible, the air inside your lungs is so you still need a way around that. As others have said you could use super oxygenated liquid to breathe. It’s been around since the 60’s I think and was used to some success in deep sea diving to avoid bends but using it ALWAYS resulted in the divers developing a pneumonia afterwards so not really worth it.