..in the days when I did the school run, and lazed about all day in the sun with toddlers pretending it was hard work.. 
I think for me this would be a serious contender:
www.gap.eu/browse/product.do?cid=89623&vid=1&pid=000453727001
loose so you dont sweat - check
sleeves so no bra issues - check
good length - yup
easy to style - check