You’re definitely on the right track – the higher protein content of the bread flour helps make your breads chewy. But you want very chewy, so you’ll have to raise the stakes a bit. Supermarket brands of bread flour contain about 12.4% protein. There are higher protein flours on the market, but you may have to search a bit. King Arthur Flour mills Sir Lancelot Hi-Gluten Flour, with a protein content of 14.2%. The company says that is ideal even for ultra-chewy bagels, so there should be no end to the chewiness of your breads.
With the added protein, however, you’ll have to work much harder to fully exercise and develop the gluten in the dough. Unless you’re a professional weightlifter or baker, you should knead the dough in a heavy-duty mixer with a dough hook or in a bread machine.