In Germany, it's very difficult, not to say close to impossible for the"normal" citizen to obtain a carry license.
You've got to prove that you're an especially endangered person (e. g. politicians, judges, jeweller), or have to carry professionally (security service, bodyguard, money transport), and in the second case most of the time the employer is the holder of the license, so that you only can carry while working.
And even If you're a legal civilian carrier, you may generally not carry at public events like fairs, carnival, festivals or concerts. If you're that endangered, you've either got to avoid these events, or take the risk unarmed.
An NAA revolver might be really easy to carry and conceal, but I would only consider this one as a backup to something more effective, or as a fishing tackle box gun.
From the choice of guns I own, the Walther PP .32 ACP would be the bare minimum and probably most suitable, concerning its size, flatness and handiness.
Or my trusted 9 mm HK P7M13, which is packing a bit more capacity and power despite being still quite compact, but requires more intense training.
But my favourite would be a small to medium frame .38 Special revolver, either an around 2" snubbie, or featuring a 3" barrel.
An older S&W Mod. 36/60 snubbie, or Mod. 10/13/64/65 with 3" barrel would be fine, Mod. 13 and 65 being more potent due to .357 Mag. caliber, but also having a more punishing recoil when using full house magnum loads.