@Lanzastar ,

How wide the pad is (unless you are literally falling off the sides) is not as important as the R-value (how insulated it is) and the length. Try to get a pad that long enough so your feet will not fall off the end. If you are winter camping, try to get a sleeping pad that has an R-value above 5. Therm-a-Rest makes some great pads (air) but they are $$$. If you are on a tight budget, you could get an air pad with a lower R-value (look at Klymit) and then add an inexpensive closed-cell pad (see again Therm-a-Rest).

Cheers!