Perhaps try a rimowa if you're prepared to invest a bit of cash in a really top end bag. This model is exactly the max size allowed by BA and you don't have to worry about carrying a soft type bag with you. It is sturdy, secure and so well made you can literally wheel it along with one finger.

Just beware that whilst this bag is the right size for BA (and Easyjet) if you travel on US carriers a lot then the bag is oversize. I've never had a problem with it and have always been let on without question in the US but it is something to consider.