I think there are very few, either you gonna use a proof of stake coin like spectrecoin that is working on both proof of stake which would make you get more spectrecoin and or you need to either use masternode for making more money which is basically something quite similar.

The mining is not a passive income believe me, I had a friend who really had to work a lot for his machines and it took at least 10 hours a work regularly and mostly even more when something broke because they are machines that work 7/24 of course they fail sometimes. I think the easiest is proof of stake because you make money on each stake and leave whenever you want, thats why I love spectrecoin.