Carefull if you add a shrimp to the Betta, it might end up as an overnite snack. Sometimes the LFS has Bettas swimming in tanks with other fish or shrimps, that would be a good inicator if they get along. If you buy him solo, sometimes the Bettas get along with other creatures, sometimes not! But that is pretty small for a tank, a Betta alone would be the best bet, with plenty of water changes and maybe a small plant that will not grow to large to take away the Betta's swimming space!