Hello r/cats

I have a seven months old domestic cat. Few weeks ago, we have noticed he had troubles using his back legs and we immediately took him to the vet. They did an X-ray and diagnosed spinal injury near his tail. Vet prescribed 3x3 shots of corticosteroids and vitamin B, and three more doses of corticosteroids in pills. The therapy hasn't shown desired results and his condition is even worse. He is barely able to move his rear(or back, not sure what's right to call them) legs, he does NOT use litterbox, which is a huge problem since he's inside all the time. Doctors said they cannot be certain of whether he will recover or not, they say his condition may stay permanently like this. His mood is still great, he tries to play, he eats regularly and drinks water a lot. I have to leave him in hallway during the night as he loves sleeping next to me and honestly, I don't enjoy being waken next to a pile of cat shit or pee.

Reddit, I need your help! What am I supposed to do? I love this furry little creature so much, and I want to help him! Is surgery an option? Something to help with his disability? Is he in pain and should be put down? It pains me to even think about this.

Looking forward to your replies.