How do you look professional in hot weather?

[OrangeMochaFrappucino]

I find it really hard to look smart in hot weather and have no idea jow to dress for the heatwave this week at work! Secondary teacher so I have to be covered - knee length skirts, nothing low cut, prefer to cover upper arms. I'm a size sixteen hourglass and found it much easier to dress well in the summer at my pre-baby 12 but haven't lost the weight I gained in pregnancy (over a year later...oops!) Am a 36HH so usually have to wear camisoles under dresses to make them decent but layering is torture in a hot classroom full of sweaty teenagers! Suggestions gratefully received!

I have been wearing cigarette pants and linen tops, usually from White Company, they have nice ones almost every year. On very hot days, I go for longer, tunic length tops (still linen).
Dresses are also good, as you can have airflow, but so many are heavy jersey. Cool cotton dresses never seem to have sleeves!
Thankfully I can wear (smart) sandals.