Hi Cajen9669,
The Beautyrest Black mattresses are made by Simmons … not Sealy.
There is more about the different ways that one mattress can “match” or approximate another one in post #9 here.
While there would be many mattresses that use much higher quality and more durable materials than the Beautyrest Black line (which I would avoid because they all contain lower quality materials that would be a weak link in the mattress) … I don’t think that you will find another manufacturer that makes a mattress that is specifically designed to be a “match” for this mattress so the only way to know whether another mattress would “feel” similar or approximate a Beautyrest Black Firm Hybrid in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) would be based on your own careful testing or personal experience.
There is more about the Saatva mattress in post #1 here and in post #2 in this topic but as you mentioned it’s a completely different mattress with different combinations of materials and components and a very different design.
Phoenix