A hot commute to a cool office
One outfit has to handle two different environments: the walk in the heat and a long time in a cooled room. Set the coverage and dress requirements first, then divide the clothing into a breathable outside base and a layer you can add at your desk.
Use a comfortable base that meets the dress code
Try a light collared shirt with an unlined skirt or straight trousers, depending on your workplace and preferences. Look at the actual fabric: a heavy lining or close waistband can undo the ease of a loose cut. If a skirt limits your stride or rides up when seated, choose a different cut or trousers. Keep shoes that are already comfortable for your commute.
Leave the indoor layer removable
A fine cardigan or lightweight unstructured jacket can go on when you arrive. Choose a layer that lies comfortably over the sleeves without pinning them at the shoulder. If you have a locker or desk drawer, leave a layer at work so you can travel lighter. A spare top only helps if you have a practical place and time to change.
Test the base in real light
Check a light shirt in daylight with the underlayer you intend to wear. Sit, reach and stand up again. If it only works under a jacket, choose another base for the commute. Save the complete combination once you have worn it comfortably through both parts of the day.