I have used one of those wíndow opening poles, as shown in photo, for many years. Must say, when I purchased it I paid less than £10. It is really great. Only one problem is that the window handle must be in fully locked position, as this pole will not work then.
So, during the summer months I never actually pull the handle down to fully locked position when closing the windows. Only lock then, when I feel that I will not be needing to open them for several months - and then do need to have one time needing to climb up (I use kitchen steps for this) to unlock them ready for use again.
Would not be without this window opening pole and would so recommend it for safety use.