Welcome to The Mattress Underground, happy to have you here 
Glad you have found a mattress that seems to fit your needs. Even though this bed is advertised as “heavy-duty” and built “to support people weighing up the 500 pounds” I’d still want to find the the mattress specifications you need to know so you can compare the quality of the materials and components to the mattress durability guidelines here. While the thicker Memory Foam comfort layer is under what appears to be 2" latex layer, heavy BMI people can wear it down if the foam density is less than 5 lbs
Bunkie boards are most commonly used on top of a platform or foundation to provide support for foam or hybrid mattresses. Each manufacturer is different in the foundation requirements for their mattresses. For example, the recommendation for Casper HD (hybrid foam/latex) is to use a foundation instead of a Bunkie board; though its more expensive, with a higher BMI you might reconsider this. I also looked at the Sleepy’s Bunkie board, and while it is very inexpensive, and reviews average medium to medium-good, you may want to look at the construction of various boards to make an informed choice. The Bunkie Board should be rigid/non-flexing or solid
A couple things to keep in mind are that using a base other than recommended can void the warranty with the mattress manufacturer, and also, a non-slatted plywood foundation restricts the air flow beneath your mattress, and can increase the likelihood of mold or mildew depending on the climate. I’d also make sure to have in writing the CS recommendation to use a Bunkie board in case you need to return the mattress.
There are many choices available for Bunkie boards of various qualities and prices. You might want to take a look at these forum posts here, here and here for more in depth discussion of bunkie boards as well as other options.
You may want to reach out to Mattress to Go, one of the seasoned mattress people that is a valuedTrusted member of our site and also a TMU mattress expert
He offers a Therapedic Bunkie Board wood foundation that you may want to inquire about.
I hope this helps,
Basilio