This forum isn't tuned to optimizing the type of pack you're looking for, but FWIW Osprey makes a travel pack that's not a bad compromise.

That particular pack is designed to convert into the type of luggage that you can safely check as baggage on a plane, train, even sometimes buses will require you to "check" your larger luggage. A typical pack, even a tough one, has a lot of straps hanging off that can catch in machinery, in which case I understand they simply cut off the offending bit so as to not slow down the conveyer. Hence this style of travel pack.