I know you said you did not want to buy online. It is hard. The key to buying online is to know the style you want and are comfortable with and to read the description very carefully. After that, you have to measure very carefully and look at the reviews to see how it runs. I won't buy anything unless there are reviews on how it runs(large/small) or if it is a brand I know. My issue is too much up top
I start looking for formals very early on to buy them. I need one about every year, and it has to be comfortable cover the girls, and not give me a migraine. And I refuse to pay a lot for it. Due to my current home location, I am usually buying my dress online. But I only buy from known businesses, no Chinese(seen too many dresses sized wrong/wrong color/wrong dress).
Good luck in your dress hunting if you have not already found one.