I've had great success over the years in new homes laying low pile commercial carpeting with no underpad. That presumes a dry basement and use of a dehumidfier.

I was hoping to be able to use a pad just so the floor would feel a bit warmer when standing on it. Are you saying no pad because of moisture concerns, or is there another reason?

Underpads absorb moisture or trap it under the pad. To put in a pad with no problem, you'll need some kind of subfloor, either drainable panels, such as DriCor, or XPS.

If you use carpet, be sure to provide plenty of mechanical dehumdification, especially in the summer months.