Tours to Bulgaria in November are not very popular. There are good reasons for this. It's too early for skiing and too late for swimming. Walks are marred by rain, and you have to hide in restaurants, cafes or museums with theaters. Which in itself is not a bad thing.
So Varna, Sofia, Plovdiv, Nesebar, Sozopol, Veliko Tarnovo and other sightseeing spots in the country will be welcome. Prices for vacations in Bulgaria in November respectively fall. So decide what you want from the rest in Bulgaria in the fall. If savings and acquaintance with the country, it's the right time.