Some of Samsonite's "normal" (55x40 etc) rollons can be bought with a matching little bag that "slides" on to the extended handle so that you can roll them along both at once.

The little bags are sold separately and are almost exactly 45 x 35 x 16 - a couple of centimetres less in each direction. They are also quite well made and have an outside pocket for documents etc. I bought mine about 5 years ago but have seen updated versions in the shops more recently.