I know exactly what you mean, Jane! I haven't done any real shopping in a long time for clothes, although I'm needing a few things. Most clothes for me are either too 'young and teenage looking' or 'older frumpy looking things'! Some don't seem to care as you said. I wear mostly knits for everyday around the house and they look good enough to run to the store in and they are comfy! I need a couple of new ones at this time.
I wear dress slacks for going to the mall or going to lunch, etc. I did wear a skirt outfit with a cute jacket for Easter Sunday. (something I already had.)
Good luck on your trip, Jane. Bet you dread all the pat-downs! I only fly when absolutely necessary and its been a couple of years of no flying for me!