Does anyone know anything about restoring/preserving old photographs and doents?

My boyfriend and I just bought a 1920 Craftsman-style house. Inside a built-in cupboard in the living room we found the original blueprints and the hand-written receipts for the building materials (lumber, etc.). In a bedroom closet we found a bag that had a note on it from the previous owners that said "Found in Attic". Inside the bag was some photographs of a little girl standing in front of the house. Based on the clothing, the photos appear to be from the late 20's/early 30's. There is also some sheet music ("Ave Maria") and some birthday cards, valentines, and an envelope that's post-marked April 1945 (with a 3 cent stamp that says "Win the War"). Unfortunately, these artifacts are literally disintegrating and can barely be touched without falling apart. These things are priceless to us and we want to have them restored to better condition or at least preserved to prevent any more rotting. We are not sure what our options are, what kind of professional would provide these services, etc. Any information is greatly appreciated.