Hi AndrewR,
It’s unlikely that you will find the same combination of materials locally with the same layer thickness and firmness levels so you would probably need to try the materials individually and then try and “imagine” what they would feel like together. The Ikea Myrbacka mattress uses a thicker layer (from the picture here it looks like it’s over 5") of the same synthetic latex over a thinner polyfoam base (although it has a quilted cover which will have some affect on the “feel” of the latex) and there are many memory foam mattresses that use 4 lb memory foam in relatively thin layers.
Yes … Dreamfoam and Brooklyn Bedding are sister companies with common ownership (see post #3 here).
The Dreamfoam Eurotop may also be worth considering and is in the same budget range. It has a 3" Talalay latex comfort layer with a quilted cover and an 8" 1.5 lb polyfoam base layer. It allows you to choose the firmness/softness of the Talalay latex comfort layer when you purchase it and for a small cost you can exchange it for a different firmness level after a purchase as well. Talalay latex is a more costly material than either 4 lb memory foam or synthetic latex but of course a Talalay latex comfort layer will have a different feel than a combination of 4 lb memory foam and synthetic latex so this would be a preference choice.
Some of the other lower budget latex or latex hybrid options are in posts #3 and #4 here but none of these include memory foam if that is important to you and you would also need to decide on the importance of being able to customize a purchase vs a local purchase that you can test in person vs an exchange policy vs a return policy and the costs involved in all of these.
Phoenix