Bella Tight Top Mattress | Premium Firm Luxury by Sleep InBella Tight Top Mattress by Sleep In Brad here from Mattress Miracle. The Bella Tight Top is the firm version of Sleep In's premium Bella line. If you want luxury materials and construction but prefer a firmer, more supportive sleep surface, this is the one. The tight top design means the comfort layers are integrated directly into the mattress rather than sitting on top as a separate pillow. This creates a flatter, firmer surface while still using