There isn’t much choice now. Though many tons of it are manufactured yearly, most of it is consumed by chemical industries. The closest thing to perfect is powder borax by 20 Mule Team, sold as a detergent booster and cleaner. Since both Europe and the US found borax potentially dangerous for reproduction (though moderately), since 2010 in the EU, it’s not sold as a generic product; analogs are mostly meant for laundry washing and cleaning.