So many people are having hard times, if one of my sons came upon something that was out of their control (job loss) and needed to come home I wouldnt have a problem with it at all. I would NOT expect them to sleep on my sofa or on a cot either. I dont like the idea of my sofa being used for a bed and I am sure it would be very uncomfortable.
I would just store my things in the attic space and as for the table I probably would just make room for it in another space/room even if it ment crowding some other furniture together.
Making over the attic space is a good idea but would it be worth the money and time, how long will your son be staying ??
I am sure the situation is just as hard for him as it is for you.