Do Air Conditioning geeks exist?

I work from home now. It rocks :) I also live in a rental property in the warm climate of Brisbane, Australia.

I wish to convert one of the rooms – westward-facing, 3 metres by 3 metres – into my office. I currently work in the main living area under a split system A/C and this has some problems that I want to alleviate.

Below is an image of the only window in this room. It has a single slider 570mm by 1450mm (the pink line) which is fitted with a security screen by pop-rivets. This window faces west and there is drainage outside.

What is an appropriate set up for cooling such a room, given that it is a rental property? I have looked at evaporative coolers and portable air conditioners but have been advised against both given our climate. It also appears somewhat difficult to use a portable A/C given the fixed security screen and the need for an external vent – can it me reversibly modified somehow? I find no other appropriate option and am a bit of a deadlock. Advice?