I'm sorry your Kokos is having mobility problems.
Does the affected foot look swollen to you, do you notice any bruising or change of colour when comparing to his good foot?
If Kokos is tame, you can try to make him perch onto your hand/finger so that you are better able to see if there is a difference in temperature coming from both feet.
You did well in cushioning the cage, keeping Kokos warm will also be helpful, you can cover the cage on 3 sides if you haven't done this already.
At this point it would be important to find out the cause for this lack of mobility on the foot and to inform your avian vet of this change.
If you have a follow-up appointment scheduled, due to the latest developments, it would be good to anticipate the appointment with the avian vet.
If the infection is indeed spreading then he needs to be seen as soon as possible.
I'm wishing your Kokos a steady and full recovery.