Diaper rash help

My baby is almost 9 months old.sleeps 6 -7 hours at a stretch at night, and 2 naps in a day. Has 40 min or so of diaper free time every morning. Its winter so we dont keep him diaper free for.more than that.since yesterday ,he had a bad rash ,the entire but was red when he woke up.(probably he pooped at night and since he sleeps in a stretch we didnt notice.).i always apply generous amount of diaper rash cream. It seems to be better today but i m worried about how to avoid this? Any suggestions ? Should i wake up in the middle of the night and change his diaper ,i fear he will wake up then wont go to sleep easily.suggestions please?