Have you officially been diagnosed as having IBS? Diarrhea and loose stool can be two big symptoms in Irritable Bowel, so I am not sure why the site you read said otherwise. You mention having soft stool in the morning, and then being fine the rest of the day. Is the movement in the morning associated with any other symptoms -- pain, cramping, urgency, etc? If soft stool in the morning is your only symptom, I'd have to agree with Keriamon and say that it might just be "normal" for you. My BF is this way, he has soft stool once or twice a day, but he has no problems with this and it's just the way he is.
If the soft stools have been going on for a while and are your primary symptom, I would say not to worry over it too much. If you have a sudden change in your BMs or they are accompanied by lots of pain or bleeding, then it would be wise to check this out with a physician. Or re-check it out if you've already been diagnosed with IBS, as the case may be.