You literally have no choice:
Volla - all phones are of the size of a frying pane.
Xperias - smaller than Volla, slimmer so better one hand handling/usage, still bad but …
Xperia 10 - everything works except of the touchscreen which has ghost touch issues, this is the biggest and only problem with this phone. It occurs on Android and SFOS.
Xperia 10 II - 3rd party caller may hear their own voice echo;The sidetone feature is not perfectly calibrated, and sidetone volume can be a bit high in wired accessories during voice calls; Mobile data does not work in 2G and 3G networks on SIM #2.;
Xperia 10 III - same as Xperia 10 II plus audio may be lost.
So in general, right now there’s no fully usable officially supported by SFOS phone.