In another reply thread I mentioned that I'm using a $50 smartphone kit consisting of a smartphone stand(Nulaxy brand, but there are dozens of similar designs) and iClever folding Bluetooth keyboard for writing. I think this is roughly along the lines of what you might want. The keyboard fits snugly in a vest pocket(it comes in two versions - I'm using the larger version with full-size keys and backlight) and gives a decent - not amazing, but good enough that I don't care - typing experience. There are many folding Bluetooth keyboards on Amazon, but this one stood out from the pack.
Combined with the stand to raise my phone I have something a bit more ergonomic than most integrated-device experiences, definitely better than what I would get from a Gemini when a flat surface is available, and I can literally throw on my vest and go for a jog and then take out the kit at a coffeeshop and lose myself in writing without difficulty. You might also need more I/O or a full PC architecture, but this setup was like a "my search is over" moment for me.
Combined with the stand to raise my phone I have something a bit more ergonomic than most integrated-device experiences, definitely better than what I would get from a Gemini when a flat surface is available, and I can literally throw on my vest and go for a jog and then take out the kit at a coffeeshop and lose myself in writing without difficulty. You might also need more I/O or a full PC architecture, but this setup was like a "my search is over" moment for me.