But the OP’s point is not to have a widely available caliber, but to shoot .357 Magnum like in a semi-auto pistol I think.
I have three 10 mm that I like a lot, found reasonably priced ammo in bulk from a guy that gave up his gun, and I reload too.
I also have a two tone SIG Sauer P229 in .357 SIG, great gun, 12 rounds in the mag with a lot of punch. For me here in Switzerland I find the 10 mm ammo is easier to find. But then I also reload the .357 SIG, and bullets are cheaper.
Whichever way you go you can’t go wrong IMO.
For self defense I think both are very powerful rounds, especially with full power. The flash and noise would be a handicap should you shoot in enclosed spaces without ear protection.
Does Austria have laws that facilitate the use of guns for self defense ?