Polh or Edible dormouse would be a good option for one of the national animals. Since it was important for decent part of Slovene territory. Also Polhovke or fur hats made of edible dormouse became important smybol in national era especially among Slovene students in Vienna. Given the density of bears, we could adopt him too.

However yeah Carniolan honey bee. Now that is quite on the top list of "national" animals in my opinion. Altho from biological point of view Carniolian bees are native in broader era not just Slovenia like south Austria, Hungary, Western Balkans, etc. but it was associated with Carniola in the past due to several reasons. Naimly it was identified as sub-spicies in Carniola and Carniolan honey bee economy evolved around "breeding" these bees en mass for foregin export hence foreginers considered them Carniolan. Thats one of the reason why Carniolan bees like to swarm (swarming in beekeeping meaning) quite often (which is considered bad in modern beekeping). Many Carniolan or generally Slovene societies, etc. adopted these bees as their symbols.

Also visually to me Carniolan honey bees are most "beautiful" tbh.