hi cowgurl, assuming your tank is heated, why not try some mollies, platties or neons? nothing that will nip his tail tho such as barbs. your local seller will always guide you at the time of purchase anyway.
you can't put goldies in with bettas as they are coldwater fish whereas bettas are tropical. wouldn't recommend mollies either, as they prefer brackish water.
I have harlequin tetras in with mine and so far no casualties, so i'd say they're a safe bet!!