Please, make a Fairphone mini. I'd buy it right away, whatever the price.

Also whatever the battery size though?

Not that I disagree. I bought a Fairphone some years ago and sold it onward because it simply didn't fit in my hand, but the phone I got instead had a delicious combo of small physical battery and terribly inefficient chipset (2019 Exynos). I'd still make the same choice but it's a considerable downside (thankfully the only downside of this phone besides its age and software support by now)