There are numerous ways to get to Slovenia, due its location you can either direct into Slovenia or one of its neighbouring country's airports:

Ljubljana, Slovenia: Easyjet fly from London Stansted to Ljubljana

Ljubljana, Slovenia: Adria airways fly from Gatwick to Ljubljana

Trieste, Italy: Ryanair fly from London Stansted or Bristol to Trieste on the border with Slovenia

Graz, Austria: Ryanair fly from London Stansted to Graz, 25 minutes from the border with Slovenia

Venice, Italy, Ryanair fly from London Stansted to Venice, 2 hours from the border with Slovenia

Venice, Italy, Easyjet fly from East Midlands to Venice, 2 hours from the border with Slovenia

Klagenfurt, Austria, Ryanair fly form London Stansted to Klagenfurt, 45 minutes from the border with Slovenia

Rijeka, Croatia, Easyjet fly from Bristol and Luton to Rijeka, 1.5 hours from the border with Slovenia