with superworms be carefull not to overdo it if he hasnt been regularly eating a few. if you give him a full feeding of it when he hasnt had superworms before he has a good chance of getting impacted because he wont be used to eating all that chitin. if he hasnt had them before only give him 2 or 3 to start and you can give more slowly, but since you only need them for now you dont have to worry about that. the best worms you can give are silkworms and hornworms if you can get them but if not just give a few supers and a salad untill you get something, since thats better then overloading him with superworms.
Mealworms will not kill your bearded dragon. They definitely aren't high on the nutrition standard, but the beardie is 16 - 18" long. Superworms are much better, but we need to clarify that mealworms will not kill him.
How old is your beardie? at 16" - 18" long he can definitely eat the medium or even large ones. I would start off slow though, maybe 2 one day, (3) 2 days later, so on and so forth.
And dubia roaches make a great feeder. Plus they are much bigger than phoenix worms, so you don't have to use as many. They are low in fat and good protein.
www.dubideli.com sells all sorts of sizes of roaches for a good price.
Small are fine, babies usually need to start off slow with them. I don't know how old yours is, but make sure She doesn't gorge herself on them, it could make her throw up.