I have managed to work with a 10kg luggage allowance for 10 days. So that is my blueprint.
I find footwear to be the heaviest item and I wear my heaviest clothes whilst travelling and minimise footwear.
As Donna says mix and match does it - and I rotate my outfits. I have never been forced to do laundry yet but would if required.
Do you have a carry-on allowance in addition?