Marc,
If this is a Zensorflex pole, you can buy another one; they're under £20 delivered; and you can use the bottom two sections of the second pole to give you another 3 foot of height.
That might sound strange, since each section is 3 foot long, but they slide into your main pole quite a long way.
It's also not exactly a waste of money, since you will have spare sections to replace any you may break on your main pole; however; the pole is extremely robust (though I don't use the 3rd section, which I suspect you do, and can still 'slap' windows shut with it).
But to be honest, a lightweight 15 foot pole will do the majority of your first floor work; it's so light that you can work with it with your hands above your head, but I wouldn't reccommend this for a lot of work (repetitive strain injury and all that).
You also may want to consider an 11 meter gangster pole for 2nd floor (3 storey) windows; I used my gangster for an external gutter clean yesturday, on a big posh house, and it was great.
I hope this has been some help.