Romance books with characters and a romance that feels mature. There is no or very low drama in the romance itself. It's often a slowburn, sometimes medium burn and feels very natural. The characters are either emotionally aware, possess a decent level of emotional intelligence, or are actively trying to communicate even if it's hard. Aside from the romance there is ample time for the characters to have growth on their own.
Keywords; Mature, slow/med burn, no drama, steady, emotional security.