We buy StoneyField whole milk plain yogurt in the large container, add agave nectar (very low on gycemic index less than honey), and add cut up fruit. I've also swirled a little jam into it to sweeten a bit. Top with granola and some ground flax seed for extra calories and fat. Also, there is a Greek style full fat plain yogurt (really creamy)...I think the brand name is FAGE.
You can also make your own. We use whole milk (we like non-homogenized), heat to 180 degrees, cool to 110 degree, then add yogurt starter (powdered starter or 1/2 plain bought yogurt), then put in containers or glass Mason jars; place in water bath of 120 degrees for 3 hours until it gels (congeals); that's it; refridgerate and eat. Amount of milk you use is the amount of yogurt you get so it is very cost affective. You just keep saving 1/2 cup of the previous batch and a new gallon of milk.