I think group or 15-20 neocaridina shrimp could be a way to go.
I have been keeping shrimp for few years now and in my experience they do love a well established and heavy planted tanks. While you may not see many shrimps, they just feel safe hiding in java moss, hornwort and they would also appreciate floating plants like salvina.
Leave some space on the bottom of the tank and place feeding dish there. Give it some time and once your shrimp gets comfortable you will see plenty of life there 🙂