Why not an xperia x compact then?
I got a used one locally to try sfosX for 40€.
I mean sure, it's a budget and ancient device, but it will work and it's small!
But if you wanna try something modern, the galaxy s10e is about 1cm taller/5mm wider than the compact, but it's a million times better.
Obviously I'm talking for the exynos cpu version, cause I think you can't unlock the bootloader in the snapdragon version.
Not sure though.

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