Have you ever tried the soft Asian style bread? For the money you buy one you can make several at home. These are very soft buns that you can even try with left over mashed potatoes. All you need is mashed potatoes with stir fried onions as the filling.
To make the buns more softer you can add bread improvers , but its not necessary if you knead the bread well.
Some ask me whether I have hidden secrets to get softer buns. I never keep any secrets. All you need to do is make them quite often. Then you become a well experienced baker. Not only they are home made but also it gives you the self satisfaction. I really enjoy baking and also love to share the correct recipes with others.