This feels a bit like one of those scenarios where you know people will inject drugs so they have to be taught how to do it in the least harmful manner.
So, as you have rejected the option of WFP (for now), the next bit is to give you tips on reducing your risks on a ladder (my drugs analogy may sound extreme but people can get killed using ladders too)
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IMO, the best one to go for is a 3.5mtr double (not 3mtr). There will be times when you need to sit the top of the ladder above the frame to reduce the angle - particularly above bays.
Get a ladder with kitemark BSEN131 (there is another one too that is OK but can't remember it).
Now I've used ladders for years and rarely stuck anything underneath for stability but the regs seem to say that you should do so. Some ladders come with such things already attached and some don't. I feel that this is a matter of personal preference. There are a number of things that can go underneath, though placing total reliance on some of them would be folly.
Top of the ladder. This next bit is important. Although many window cleaners don't bother, getting "ladder mitts" on the top of your ladder will decrease the risk of it slipping sideways by a considerable margin (it doesn't work if the sill is iced up though). If you leave them on, it will mean carrying your ladder around open by one rung. Do use these - every time.
Avoid decking - particularly if it's damp/wet. Avoid mossy patios.
Do invest in a pole on which you can place an applicator and a squeegee (check out the varieties that swivel). This will allow you to do some kind of clean on most windows where access might otherwise be dangerous.
There are various things that can go under the ladder to help with safety. Plenty of info on the net.
Take a look at this page:
http://www.soapnational.co.uk/acatalog/ladder-accessories.htmlI particularly like the one for decking. That's a new one on me.
Stay safe.