Just searched on Amazon for something similar and this popped up:

KROSER
Carry On Underseat Multi-functional, 16-inch Underseat

It is basically a wheeled tote that stacks. Cheap but fills the need.

Go with a backpack. I normally don’t check luggage but when I do I’ve found I need a backpack rather than a tote to distribute the weight. Mine is a Lo & Sons that I also use for work. I can also do a lightweight tote as my second item as long as my laptop and heavier items are in the backpack.

Steve Madden has the stackable strap

https://www.travelandleisure.com/style/travel-bags/best-underseat-luggage

Anonymous wrote:No one actually read the OP. She wants a wheeled carryon that she can somehow attached to her wheeled checked bag.

Does such a thing even exist?

I’ve seen flight attendants with this setup.

Underwear wheeled is keywords

https://www.amazon.com/Hanke-Underseat-Suitcases-Lightweight-Airplanes/dp/B0CLLB4N38

Stacked seems tough though.

Anonymous wrote:

Anonymous wrote:I travel every week for work. I never check my bag unless I’m on a long overseas trip. For a 4-5 day trip, I have a Timbuk2 backpack and a small Ricardo/Samsonite 4 wheel roller from Costco. I view these suitcases as disposable and replace them every 3-4 years. I don’t want to call attention to myself using a $1,000 suitcase. Also, I’ve had to replace a suitcase during a trip once because the wheel broke. Luckily, there was a Costco nearby and they exchanged it. Even if they didn’t take it back, it’s $70 how a new one.

The thought of sending suitcases to the landfill every 3-4 yrs makes me shudder. Just buy a quality suitcase and stop wasting the earth’s resources. You don’t need to spend $1k to have a quality suitcase. Stupid.

Save the histrionics. The CO2 for just about any single flight dwarfs the environmental impact of their suitcase.

I use a rimowa as my carry on and I fly charter/PJ.

If you have enough for a duffle why can't you just take a regular wheeled carry on? You can still attach it to your larger suitcase when you pick that up at baggage claim. NOt seeing why it has to be a duffle.

https://www.calpaktravel.com/products/hue-mini-carry-on-luggage/emerald

No one actually read the OP. She wants a wheeled carryon that she can somehow attached to her wheeled checked bag.

Does such a thing even exist?

For bigger trips, I do check a large luggage. I try not to haul too much on the plane if I've already checked a luggage. I use a Tumi Just In Case Tote to carry a spare set of clothes among other things, and that bag has been very useful.

I buy Samsonite (usually it comes in a pack of a full sized suitcase and a small carry-on cabin suitcase) from Costco. Costs the same as buying one full-sized suitcase at any other store.

Normally, while travelling I need from 1-3 full sized suitcases and one carry-on cabin suitcase. So, I have a carryon for every full sized suitcase.

I have been able to utilize the smaller carry-on cabin suitcases as storage for jewelry, important documents and medical gadgets repository at home.

Rimowa is absurdly expensive for what is just a normal carryon.

I have a Biaggi carryon that can convert to a checked size I like for trips—if I am bringing back souvenirs or work stuff, I can easily expand it and check. I can travel about a week with it.

I also have an Biaggi under seat bag I love. When I travel I want all my stuff with me. Snacks, kindle, chargers, meds (I have a serious health condition and can’t risk being separated from meds). Neck pillow, chapstick, etc. I like it all within reach. It slides on the roller convertible carryon as well so I am not carrying anything.

I have a North Face backpack I got for free at work and use that as a carryon. Before I got that, I used a free tote I got from DSW about ten years ago - it's great because it has a zippered compartment on the bottom for shoes.