I don't want to harp on but get a pointed extendable ladder.
They are so much more stable and are much easier to use on uneven ground and if positioned right, the ladder cannot move sideways. Also, if you keep the rubber bit clean, it doesn't mark window frames plus you've many more options of where to place the ladder.
I now wouldn't use a normal ladder for anything especially window cleaning. Once you've got used to an A frame, you'd never go back to a normal ladder. Ask any w/c'er who uses one and you'll get the same answer.
Cheers