Any glass / flat top digital kitchen scales will do , so long as it can weigh stuff as heavy as a 2kg and gives weights to the gram.
He looks fine to me.
I VERY STRONGLY SUGGEST that you ditch the sand you are using for his substrate - it's a very bad impaction risk as well as the perfect breeding medium for viruses, bacteria and fungi because it's impossible to keep clean and dry.
Bearded dragons do not live on sand in the wild , there is very little sandy desert in their natural range.