i wouldnt bother in a five gallon it will only end in heartbreak, but every betta is different they say. if you do try it keep the betta in another container for a few days then add him to the tank with his new friend already there. i would only try snails or shrimp. i had a betta that forced 4 cherry shrimp to jump out of the tank in suicide. I think the best tankmates are those that have 'play dead' defences like banjo catfish and khuli loaches but youll need 15g for them and plenty hiding spots.