Oh no, poor you and poor Oran!
My brother's dog (working cocker x working lab with hugely high energy) has just had surgery for hip dysplasia and wasn't allowed to walk at all for 10 weeks. So it was lots of training for mental stimulation - but for things that didn't involve lots of movement or running around like barking on command. It sounds like you have this covered already though!
She also had lots of chews (low calorie as she wasn't burning energy) like deer antlers.
Is he happy in a crate? My brother's dog is, which made it easier, but it wouldn't work for every dog.
Hopefully you will get lots of good ideas from people here to keep him entertained and you sane