Best Way to Travel with SimplyGo

Hi!  Have had the SimplyGo for about a year now and have been toting it around using my old EverGo cart.  We worry that the cart will break at some point, as we have had it since 2008.  We are exploring different options for toting the SimplyGo around.  I mostly only need it for airplanes and when I remain at altitudes of 3500 feet or more (live at sea level).  I'd appreciate any suggestions folks have about a great way of toting the SimplyGo.  I have put it on top of my 21" wheeled suitcase, but H finds it too topheavy and doesn't like it (it does tend to fall over).  I don't like the new SimplyGo cart as much because the wheels are larger and I don't think they will fit as easily underneath the seat; the flight crew insists that we do NOT put the wheels in the overhead bin.

Did check out Costco, Ross and Macy's to see what they had that might be able to support the 11.5 pound weight of the SimplyGO, perhaps a spinner that is a tote or briefcase, but had no success.  I think it would be nice if it were a spinner so it could go down the ever narrowing aisles on the plane.  There were very few 2-wheeled options that were somewhat interesting but nothing that really seemed right.  Any suggestions from folks who have found things that work great for them in toting something like the SimplyGo @ 11.5 pounds, especially for plane travel?  Thanks!