Hi Jackery, and welcome to the forum!
I make yoghurt so often that I know the recipe off by heart, and can't remember where I originally got it from, so apologies to the original poster.
I measure 800 mls milk into TM bowl (have used both full cream and semi skimmed, but haven't tried skimmed), and add about 40g milk powder. Mix on speed 5 for a few seconds to combine, then cook at 90 degrees for 15 mins on speed 3.
When it has finished, take the lid off the bowl and leave to cool until temperature registers 37 degrees (I have forgotten sometimes and left it for too long, I just cook for a few minutes at 37 degrees to bring it back to temperature.) and then add about 100g live yoghurt and mix at speed 5 for a few seconds to combine. I use a pot set yoghurt for the first time, then use some of the previous batch when I make more. I have kept it going like this for over a year sometimes, but if the yoghurt starts to taste sour or doesn't thicken properly, I buy a new starter.
With the starter added, cook for 2 mins on 37 degrees at speed 3, then pour mixture into an Easy-yo container. Fill the thermos with lukewarm water, pop in the container of yoghurt and leave overnight to set. This always results in a thick and creamy natural yoghurt, then I add chopped nuts or fruit purées to the finished yoghurt.
If you don't have an Easy-yo thermos, you can set the yoghurt in the thermoserver, but I haven't tried this.
Hope this helps,
Sue