Hi Roddy,
The Ultimate Dreams isn’t a single mattress because you have the option to choose the firmness of your comfort layer so there wouldn’t be a single mattress that it “matched” or even “approximated”. Post #2 here though should be helpful in how to find mattresses that would be similar in design (if not in firmness levels) and could help you make your firmness choice.
If you let me know the city or zip where you are I’d be happy to let you know of any options in the area that you could call to see if they had a mattress with a similar design that you could use as a guideline.
Phoenix