Go ahead and wear geeky t-shirts, you just need new ones and the local equivalent to Walmart should have them. Hit the PJ section for some blank ones.

I like Woman Within, but you don't sound like a plus-size and dressing too old might be as odd as dressing too young.

Maybe you could find someone who would volunteer to be a personal shopper?

One item of clothing that I like to wear is a cargo kilt. This one is cheaper than the one I got... Oh, that cheap one isn't full-cotton. Try this one if the thought interests you.