I am sorry to hear this. I don't know much about it..at least in dogs, I know what ruputured discs do to a human. If he does need to use stairs to go outside..get or build a ramp for him. Max has calcification in his neck and is not suppose to do stairs so my husband built a ramp off the deck to the yard. Also raise his food/water dish up. They make ones that are for low rise dogs. I got mine at PetSmart. I would talk to your vet about acupuncture for him to control any pain he may have. It's pretty much one of the only pain abatement things that has no side effects like meds do. And it's something they can continue for years unlike many medications.
I tried it for Max with his neck as a last ditch effort...it was that or put him down, he was in that much pain and meds did nothing. Best thing I ever did. He has gone twice,1st session was 8 treatments and the 2nd a year later for 4 sessions in 3 years. We are coming up on a year after the last time he went. I can say it was the best thing I ever did. I have severe back problems including a fusion. When I saw what it did for Max I started going for my pain. Completely stopped the pain shots and I no longer use prescription pain medications...only Aleve when necessary.
I would be very careful with him both now during the crate rest and in the future. Many times with IVDD if they move wrong, jump wrong, etc they can become paralyzed and need immediate surgery. Often if he is a surgical candidate they can completely fix the issue with a rather invasive spinal surgery but an excellent chance of a full recovery. Often when it is a slowly progressing issue surgery isn't an option and pain management and limiting strain on the back are your only options. I agree with acupuncture. We did it with my last two dogs to manage hip dysplasia and one of my dogs for a neck injury. Worked really well for one dog, and not as much for the other, but both saw improvement at least for a short time after treatments.
Waffle has mild IVDD in his neck. We manage it with an anti-inflammatory (Deramaxx, but now Previcox since the Deramaxx manufacturer is in limbo) and crate rest. It flares up when he strains too much--if he gets picked up and struggles or something, he will inevitably injure himself and need to take it slow for a few days. Funnily enough, we can play tug and he can get slammed around and be fine, but if he moves his head the wrong way after being picked up, he's down. You will get good at knowing how Kirby feels on any given day after he recovers. You'll know when he may have tweaked his back and should be kept still so he doesn't blow it out again doing something strenuous. You may have to stop him from doing certain activities, but life after recovery will be mostly the same if you're vigilant and can read him well.
Praying for Kirby...and you! Kirby needs your love and support more now than ever before. I know nothing of ivdd, but your vet and friends here on MyCorgi will be there for you to encourage you and strengthen you when it is needed. Good luck and BLESSINGS!!