Home-make yogurt: add sugar / something else with the starter?
The statement "so that bacterias would have something to eat" is incorrect on several levels- including grammatically.

Bacteria already have plenty to eat. There is a lot of sugar in milk. Cow's milk is 4-5% sugar. Additionally, giving the bacteria more to eat would allow them to create more acid and make the product more sour not less.

The bacteria used in yogurt making are lactobacilli and prefer munching on lactose anyway.

That said; Lactose tastes less sweet than the sucrose in table sugar. Adding sucrose will make the yogurt sweeter if that is your taste.

Making the yogurt thicker is done by 


accurately controlling the fermentation temperature, 
using higher fat milk, 
adding protein in the form of dry milk powder, 
or removing water after fermentation.  


When I have added sugar to my yogurt it has not had a noticeable effect on the texture.