4.8 m will do most ( if not all ) 1st floor windows
have you thought of ditching the ladders and just getting stright into WFP
small RO to start ( 80 quid on ebay )
rain water butt ( 25 quid DIY store )
fishing pole ( 25 quid )
Brush ( 15 quid )
backpack ( 100 - 125 quid )
sack truck for backpack ( 25 quid )
various pipe and fittings ( 25 quid )
6 X 25L barrels ( free from car wash )
complete setup for under 300 quid
you will spend that on a decent set of ladders and roof bars ( well allmost )
still buy the trad kit for downstairs windows, just WFP the upstairs, tell the customer about the Working at height regs and they will accept WFP upstairs ( blame them damm europeans

)