Hello Michelle
Sweetener 955 is actually Splenda and it's worth reading this article about it:
http://www.splendaexposed.com/ and deciding if you wish to continue eating Tamar flavoured yoghurts.
It's best to keep to unflavoured natural yoghurts which don't contain any sweeteners, even artificial ones which, among other things, are known to raise insulin levels the same as sugar does and so negate any efforts to lose weight. You can also add berries to natural yoghurt which will give some sweetness without side effects. You can also add some dextrose to natural yoghurt if you are craving sweetener.
David has listed all artificial sweeteners under "Your call" and would very rarely use them himself. Personally, I find that I have become a mainly savoury eater with rare excursions into dextrose sweetened desserts if we have guests.
Some people use Stevia as a sweetener, this is also in David's "Your call" list as he feels that not enough research has been done on it. Stevia, like sugar is plant based.
cheers
Freda