Sleeveless and shorts is ok for usual days but for temple visits, temple will require you to cover up with scarfs. It is ok if you don't mind.
Another thing to add. Taxi fare. They like to quote us, tourists high prices. Either bargain for a reasonable fixed price or go by the meter. Otherwise, taking the tuk tuk for short distance is fine. It is cheaper.
Also, taxi drivers like to bring you to shopping malls meant for tourists before bringing you to actual place. Insist that you do not want and tip them a little and they will give up. They earn a commission for every tourist they bring there.
Thank you all for these tips. We are so ready now to see Bangkok yipeee! I told them to bring leggings and scarfs coz we'll be going to see lots and lots of temple. Oh by the way, which temples is a must to be visit?