Hi noahsi.
Welcome to our Mattress Forum. 
It is always a downer when a mattress you know works well for you goes out of production. I was able to pull up the specifications for The Best Mattress Ever (you’re correct, they’re trying to rebrand their hybrid as their original “Best Mattress Ever” - I couldn’t tell you why though). You are not alone. Many people liked the mattress and it’s too bad that they reworked and changed materials and specs.
The version you have (medium firmness) is 10" with 2" Talalay (28 ILD) followed by 2" Dunlop (32 ILD) and then 6" of a 2 lb convoluted polyfoam core (around 32 ILD). This is good startup info as to what works for you. Link to BBs archived discontinued Best Mattress Ever.
It looks like you’d rather stay with “what you know” in terms of feel with an all-foam configuration. While I see no need for you to try and learn to love a hybrid mattress, Depending on your budget I would not disregard them altogether as there are no real downsides to using a pocket coil support Also Pocket could have many advantages in terms of longevity, temperature regulation, motion isolation, conform well to different body types and sleeping positions. etc. There is more about an innerspring/latex hybrid vs an all latex mattress in post #2 here.
Because every layer and component in a mattress can affect the feel and performance of every other layer and the mattress “as a whole” I’d say that you’d have a different experience with any of Brooklyn Bedding’s other lineups. If you’d like to venture into some trial and error experiments I’d make sure to find out information listed here so you can compare the quality of the materials and components to the durability guidelines here to disqualify any mattress that has lower quality materials or weak links in a mattress that would be a cause for concern relative to the durability and useful life of a mattress.
This said because you know the ILDs/foam density of the configuration you have; it wouldn’t be especially difficult to recreate this mattress yourself with DIY components in a King size - although I’d recommend moving to an all-latex system if budget permits as it’s going to be more durable over time and respond better than polyfoam core.
A DIY is certainly an option and can get a bit complex but it is usually a rewarding option if approached in the spirit of adventure. You’d be able to tweak and adjust the mattress to your liking, and can do a side-by-side split if your partner would prefer a different feel or firmness. If that’s the route you choose to take, there are experts and resources on TMU to help, if you chose to go that route.
Here are some slicked experts that can offer personalized guidance on how to do this whether you buy from them or not.
Deborah at DIY Natural bedding
Ken at Arizona premium mattress company is very skilled at helping consumers with their DIY
Shawn and Rodger at Latex Mattress company
And of course, SleepEZ can help with building a DIY as well.
You can also “build a mattress” on [URL= https://www.flexuscomfort.com/natural-latex-mattress.html]Flexus’ website[/URL], with the option to buy the base recommended for the mattress.
Regardless of which mattress you choose, it’s important that you have a detailed conversation with the knowledgeable and experienced retailer or manufacturer who, and provide them with good information about your body types, sleeping styles, general preferences and history, some general information about mattresses you have tested and done well with, and any other specific information or circumstances that could affect your choice of a mattress.
In your case, being able to give specific ILDs would be a great help to them in assisting in choosing or configuring your next mattress.
I am assuming you probably meant “now” instead of “not” ….otherwise the dots don’t quite connect given your normal range BMIs, II’s be surprised if you’d be already in the market for a new mattress after not even 5 years of life from the original version of the Best Mattress Ever. Correct?
This also comes down to the mattress you buy. The manufacturer or expert helping you configure your mattress will have recommendations - and in some cases, certain bases may void a mattress warranty, so you’ll want to keep that in mind when you’re speaking with whomever it is you choose to buy your mattress from. If it were me because there are quite a few variables depending on the type of mattress you end up with, I would separate the purchase of the foundation from that of the mattress and first ensure that your new mattress works as expected after you’ve had the chance to sleep on it for a while even if it means placing the mattress on the floor for a certain period before moving ahead to buying a platform/foundation. I am saying this because of the lower back pain you mentioned which may have been caused by improper comfort/support or a sagging sleeping surface or both.
I hope this helps. I look forward to any future updates or questions you may have.
Phoenix
Note added later: As I am intermittently working on posts today I didn’t notice that you deepened your research. Good to see that you are on the same wavelength and discovered on your own some of the directions I’ve indicated in this post. Good Job!
You are quite right! Both Luma Sleep and Nest Bedding are very good options depending on the type of mattress you decide will best serve you. Both have very good workmanship and design and as you probably noticed they are trusted members of this site which means that I think very highly of them and that I believe they compete well with the best in the industry.
Many mattresses are designed this way to offer more options for fine-tuning comfort support. There is no downside to having a 2 pieces mattress. It would be the same as having a topper on a base mattress and fitting a 2 piece bed with sheets’ is not more “awkward” than fitting a one-piece mattress.