I have some family connections with the Laundry business, but I was not involved myself. The only advice I can give is :-
1. Do NOT get it Dry Cleaned, and under NO circumstances use a coin-in-the-slot Dry Cleaning machine in a Launderette. The fumes left can be Fatal, and there are several stories of people being killed by faulty Dry Cleaning machines when cleaning Duvets.
2. Treat the sleeping bag like a feather filled Duvet and look for a cleaning company that washes Duvets. They will have the correct professional cleaning machines and staff you need to do the job. Home washing machines are way too small and even those in Launderettes are sometimes too small. Best to contact a Laundry company that cleans Duvets to do the job for you, and phone around for a good deal.
Hope this helps.