No bettas who are males can not live with another male, even a female unless you are planning on breeding but you must have experience, and know what your doing, and taking risk of ripped fins, and fighting and maybe losing your betta if you are going to 'breed.' Anyways that's not the point, only female bettas can live together but that's also with experience, and it's preferred to be with 4 - 6 females or more.
Your betta is happy the way he is, I am sure he doesn't need a companion, if you do want to get a companion I would recommend a snail, depending on how big your tank is, is it cycled, and is it heated? If it's less then 5 gallons I do not recommend getting a companion. Sorry if I am being rude.