Plus time.
I’ve tried other milks with varying results: some product yogurt like drinking yogurt, some are closer to Greek yogurt.
2nd and 3rd generation yogurt starter should be fine, esp. if you’re making it on 3rd day or shortly after incubation. It keeps really well.
If you’re only eating yogurt once or twice a week… it’s probably better to start from scratch each time. In that case, I suggest just using pots of live yogurt from the supermarket as your starter. Just make sure they are ‘live’ and don’t have additives.