For routine 1st floor windows, a two tier ladder would be best.
Ensure you don't buy a light-weight set from 'B & Q'. Your ladders should be safety tested to BSEN 131 - they should have yellow feet.
When the feet start wearing down, change them regularly.
Don't be like some of the local window cleaners I know who wear the ladders feet down to the alluminium; and carry on using them.
I've fallen from B & Q ladders and it wasn't a pleasant experience.
Also do a search on this site for ladder mats and a Rojak ladder stopper.
Both are top bits of kit.