What dark chocolate is good to use as all of them are very high in sugar and sat fat etc. Thank you kindly in advance
You are probably best looking at the labels on the different brands, if you have specific requirements. There are a huge number of high cocoa dark chocolate brands around now, with every supermarket doing their own brand, and all the big names offering cocoa content from 30% right up to 90%+
Generally speaking, the higher the cocoa content the lower the carbs, since there is less room left for sugar.
Regarding the saturated fat, I see no reason to avoid it, but if you want to do so then again, you would need to look at the various labels and make your choice. The supermarkets list the carb and fat content of all their products in the nutritional info online, so you can easily look there.
Personally, I add double cream to my cocoa/erythritol/hot water, so the presence of saturated fat in the chocolate is insignificant compared with the gorgeous sat fat in the double cream.