be on to a good thing idiom informal
过上舒心的日子;找到好工作
to have an easy and pleasant life or job in which it is not necessary to work hard
He's on to a good thing, he has free accommodation in return for a little easy work around the house. 他可交了好运，只需要给房东做一点容易的家务就让他免了住宿费。