This is an excellent book of eye witness accounts of the invasion. Compiled, edited, and translated by Antony Brett-James and published in 1966. The accounts are from officers, generals, diplomats and enlisted men on both sides of the conflict.
Here is an entry from Paul de Bourgoing, a second lieutenant in the Young Guard in 1812:
“Nothing can convey the enthusiasm with which the young men prepared for this distant expedition. I was nineteen at the time. We were so confident of success that, according to our calculations of promotion and ambition, we regretfully considered this campaign as the last in which the Emperor would take his chance in battle to become master of the world.”