Narrow stairway. Prefer extra rinse, front loader.
Know of any brands, models?
Ever tried ariston?
I really don't know anything about Ariston and find looking for the right appliances to be daunting. There are so many options now and new manufacturers showing up. A search listed the brand at most of the stores. Ariston is also shown as offering a huge range of appliances which include commercial ranges, double drawer dishwashers. They must be widely used. Link below is from an appliance review for Aniston and Haier (24").
Here is a link that might be useful: Review
Try searching in the Appliance Forum or the Laundry Forum. Maybe someone there knows.
My Bosch Axxis fits in a 24" wide space. Both washer and dryer are stackable.