Shorts for either men or women are not appropriate in Bangkok. They are considered resort wear. Yes, you'll occasionally see a farang in shorts, and they will tell you no one said anything to them about how they were dressed (unless they went to the Grand Palace/Emerald Buddha where they would have been denied admission), but you'll rarely see a Thai in shorts in the city. And the locals are mostly too nice to say anything about the inapproateness of one's attire.

If you want to get in contact with one of the drivers/guides for Bangkok. do a search on this board (type in Bangkok and the guide's name in the search box) and you'll find contact info. Read a few of the reports about each of the guides so you get a sense of their styles and strengths. I'd suggest one day (perhaps two) with a driver or guide in Bangkok. You'll want time on your own as well.