A quick tip that might help: Don't get the paratroopers until you can afford all the way up to the exploding pants upgrade; the paratroopers only add an extra pig to kill.
A great way to beat the final boss is to wait until he sends a wave of ballista and then kill all but one of the ballista and hang back while gathering resources. (I found that Rose Magma Heart worked the best because of her meteor attack too.)
But in same time without paratroopers a sky levels much harder to complete :)