With Wizz Air you can travel to the Bulgarian cities of Plovdiv and Varna during the winter. Return tickets from Bratislava to both Plovdiv and Varna can be purchased for 33 eur - this time also for WDC members at the same price.

See also accommodation prices in Varna and Plovdiv.

You can rent a car and drive along the northern Bulgarian coast or take the train inland.
From Plovdiv, you can easily take trips to the surrounding mountains or historic towns and explore Bulgaria outside the high season.