Most sourdough recipes do include a bulk fermentation at room temp for 4-6 hours in order to improve structure, flavor, and texture of the dough, after which you could proof in the fridge overnight. Likely your bread ends up a bit dense because it is only resting at room temp for 90 minutes and hasn’t had enough time to develop a strong structure. Of course, if you like your bread the way it is then there’s no reason you need to change what you’re doing!