I don't know what your climate is like, but where I live it's very hot in the summer so I spend basically ALL summer wearing cargo pant cut-offs and cargo shorts. They're great because you can find some that fit in your hip/rear zone while not having to worry so much about how long they will be since leg length is a matter of preference and style.
I think the best thing to do when you're first trying to figure out your size is go somewhere that you know will be pretty safe or have employees who are apathetic enough not to care. Thrift stores and Walmart have always served me well in that regard. Then try on a lot of stuff and get a general feel for what styles and sizes work best for you. For example, I know now that my hips are a 32-34 and my inseam is 30 because I tried on just about every pair of pants that they had at Walmart.
