Looking for an expandable, two wheeled carry-on bag I can use internationally -- and Icelandair/Ryanair seem to be the most limiting carriers with their size constraints of 21.6 x 15.75 x 7.8 inches, or 55 x 40 x 20 cm, including handles and wheels.

This last dimension, the 7.8 inches or 20 cm depth, is the one that seems to rule out so many bags available here in the US, such as Rick Steves' best selling rolling carry-on, which otherwise seems like such a pragmatic solution. It is listed at 9 inches, just a bit too thick!

I have a cheap bag of a conforming size that I bought a few years back in the UK and used many times on Ryanair and Easyjet. But I don't expect it will hold up if it ever has to be checked in the hold, so I'd like to invest in something more durable since we expect to do lots of travel in the next three years.

Just wondering what others have done to conform to the international measurements (especially the 20 cm), as I know from experience that carry-on sizes and weights are checked, maybe not all the time, but I want mine to fit!