This is probably the best weight savings/cost.

There was a time, long ago, when essentially the only people who had wheeled luggage on aircraft were flight crew. Everybody else seemed to have soft bags with carry straps - sometimes backpacks, but usually clamshell or double-clamshell with a shoulder strap and sometimes stowable backpack straps. The transition happened some time in the last ~25ish years. Some time around 25years ago I received a bag from Travelsmith as a gift that was called "The ultimate carry on" or something close to that. Double clamshell, external large and small document pockets, internal side pockets, one of the compartments expandable for conversion to checked, and stowable backpack straps and a regular shoulder strap. It's still in great shape after decades of use, and I haven't seen anything similar in years. It fits anywhere because it's squishable, so it never ends up on the ramp-check cart. It's 1.8 kg empty, and I could probably drop a few hundred grams by removing the backpack straps that I never use and leaving the strap behind (it has handles, too). I have a duffel from REI that has comparable storage flexibility that comes in at 1.4 kg. You can probably find similar duffels made from lighter weight materials that come in under 1 kg.