Wow dude I know your pain! Litteraly!
I also have Degenerative Disk Disease and have already had surgery on the L4, L5-S1.
From my personal experiance, the cruisers hurt more. Sitting in an upright position I end up using the spine as a shock absorber regardless of however cushy the cruiser suspension.
I have spent 3 years doing all factory demo rides trying to find a decent cruiser but amost all are not comfortable with me. I end up in pain after 50 -60 miles.
While riding the sport bikes, I am slightly hunched over alleviating direct pressure on the spine. I have learned to use my legs, core muscles and arms to help with this. (I have also worked with a personal trainer that specilized in back rehab exersices to help build the muscles in my core and around the spine.)
I will have pain in my back for the rest of my life. Some days the pain is managable, and sometimes not so much. However by doing the exercises and adapting myself a bit for the ride, I am able to make it worthwhile.
A couple of weeks ago I did the Midwest Meet & Greet in St.Louis. The day I did the Bixby run was a 420 mile ride day. I was more fatigued than in actual pain.
I hope you can work it out and enjoy your ride on whatever you chose!! Good Luck!!