I just learned of a model of floor chair called the Eco Backrest by Carolina Morning. Could this be a good option for stretch sitting? https://zafu.net/ecobackrest
That does not look like it would be good for stretchsitting--too reclined and too puffy in the lumbar region. If the Gokhale Method Chair is out of your price range or otherwise not what you want, I would recommend just a normal folding chair with a stretchsit cushion over these other options.
Gokhale Method Instructor
Thank you Abeja!