Unless you are going to be spending a significant amount of time camping, buying expensive sleeping bags is really unnecessary. Even if your old and musty sleeping bag is rated for below freezing temperatures, it is excellent padding for the ground even when it is hot outside and you will feel comfortable sleeping on it.
One of the most important things to remember when camping is to keep yourself relaxed. The entire point of a camping trip is to get away, so if you are finding yourself stressed by something, leave it alone and go enjoy nature until you are able to calm down. This will keep you happy and safe.