I usually add blueberry or other berries (fresh but frosen, without sugar), and banana. I use some of the yoghurt as a smoothie, so I put berries and/or bananas and yoghurt in the blender. Super delicious!
The SCD diet has a lot of recipes how you can use the yoghurt.
And yes, you don't have to buy those starters, you can also use yoghurt with good bacterias added, bought in a regular store, just look if you can find yoghurt without sugar but containing at least lactobacillus caseii rhamnosus, lactobacillus bulgaricus, streptococcus thermophilos and lactobacillus acidophilus. The three last Elaine Gottschall mentioned as a dream mix.
There has been a scientifical investigation on lactobacillus caseii. They found it to benefit the intestines.
Good luck! From Ingrid