I‘m glad your dear son is doing a bit better op, it’s a horrible thing he’s going through and it’ll take time. I know you’ve mentioned another dog, and you know your son best, but I just wanted to share my experience, for what it’s worth.
When I was 10, I got my first dog, he was amazing, I was obsessed. He was stolen from our home when I was 13 and I was bereft, properly heartbroken, not eating, not sleeping, same sort of emotional distress as your son by the sounds of it. My mum suggested another dog, and I thought it was a good idea, but once we had her, I admit I sort of hated her for not being MY dog, iyswim. We couldn’t bond and I felt appallingly guilty about it, and in the end, she became my brothers dog, really. I still feel bad now for not giving her my best (and this was 20 years ago!) but I got another dog, for myself, a year later, and it was a different ballgame. I adored him, every day of his daft little life until I lost him 3 years ago.
I just feel that maybe more time might be a consideration. I’m aware it’s not my place, and ultimately you know best, your son, your dog, your home. I just wanted to, gently I hope, add a viewpoint.
Best of luck with it all.