For oatmeal, why not buy the sugar-less kind & just add the amount and type of sweeteners that you would like, to taste?
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Last time I was at a Sainsburys, I was checking out all the different kinds of muesli and granola stuff they had. Maybe try some of those to see if there's any you like? It may not be Kashi, but maybe you'll find a new favourite?
The cereal selection at Morrisons seems a bit more limited, IMO.
Or maybe see if there's a health food shop in your area & what products they offer?
I don't like Weetabix either! I was eating muesli (Alpen no added sugar) but I've kind of gone off that, and either I have porridge or something else (not cereal) for breakfast these days. I've never had Kashi, so I'm not missing that.