Glass and backing needed

My driver side mirror is cracked. The backing is loose from the mirror cover. Can I purchase the glass in the backing for a 1999 Yukon Denali, or do I need to purchase the whole mirror assembly?

After I broke the side mirror in my father-in-law's van I took it to a local glass shop. They cut a perfert piece out of a section of mirror and glued it in place. Very cheap to do and is still holding after a year and half.