The hammock will hang the same no matter how high or how low the ceiling if you maintain the same suspension angle. The only thing that changes is how long the suspension lines are. So for a 7' ceiling you'd move the attachment points in 2' from what I use for an 8' ceiling. Experiment in the basement with various distances, find what's most comfortable and then recalculate the distance for your 8'8" ceiling.
To make the suspension reasonably easy to adjust, take a length of rope and feed it thru the pad-eye hanging it from it's midpoint. Double up the rope and treating it as a single line feed it thru the eye of hammock and tie it off with a sheet bend or double-sheet bend. Adjust length as needed.