I think u should be able to make a bag that u could collect the ender dragon egg and then u could incubate it and get a pet ender dragon that u can fly with u into the overworld. There should also be dragons in caves that u can steal eggs from and incubate them. They would be smaller but could ghast fireballs
Dragons in caves can be found with a lot of hidden treasure in there lair and there could be a nest full of spotted eggs. The dragon in that cave will automatically try to kill u but will leave there cave at noon until dusk. U then could steal thier eggs. The mother dragon would automatically begin to go back no matter what time once u steal an egg. Killing dragons will give u scales that can be used for armor. Dragons could start as a smaller version of the ender dragon then they would grow larger and then u could fly on them by using a special dragon saddle. The basic dragon would be smaller than the enderdragon and would do less damage but can shoot fireballs.