Internal frame backpack or external frame? If internal, it needs to fit the available space(s); more info needed to advise (which make & model). If external frame, size is pretty much machts nichts. In either case, for Kansas use I suggest carrrying it in an inexpensive drysack from Outdoor Research or Sea to Summit - once you pick the bag I can help you figure out which size drysack will work.

How much weight are you aiming at and how long will the trips be? Minimum temps you may camp in? Budget? You might not need an actual sleeping bag or you might do well with an overbag sized to fit you (which can be paired with another conventional bag later for colder weather use).

You a cold sleeper or a warm one? Going to tough it out in sweat-soaked day clothes or skin down to sleep or change to non-sweaty sleeping underclothes or ???

We can help you figure something out.