i'd go with just slightly bigger then a small rat. your ball is around the same size as my blood was when i switched it to rats. by slightly bigger i mean maybe a week older rat and since i switched it to larger prey my blood has shed every month since only problem is live rats cost a Lil more then frozen at least here where I'm from your best bet is to find a snake breeder close by how breeds his own rats you might have to drive an hour to get to there house but guy i found that i get my rats off of is half the price of getting a rat at the pet shop