Seems obvious to me that if you'd like your spine to remain in something close to normal anatomical position, the mattress had better be firm enough...
You have to substitute carbs with fat. More satiety, fewer calories. And protein MUST be sufficient if you're going to train while you're doing this....
If you let a doctor cut on you to fix something that is not really a problem, you will have a brand new problem. And if you think that any minor pain...