Hi jessa:
Thank you! 
Congratulations on the weight loos. Keep up the good work. :cheer:
Brooklyn Bedding is one of the members here which means that I think highly of them and that I believe that they compete well with the best in the industry in terms of their quality, value, service, knowledge, and transparency. All of their mattresses use high quality materials and there are no lower quality materials or weak links in any of them so they would certainly make a great quality/value choice.
When you can’t test a mattress in person then the most reliable source of guidance is always a more detailed phone conversation with a knowledgeable and experienced retailer or manufacturer (like you already did) that has your best interests at heart and who can help “talk you through” the specifics of their mattresses and the properties and “feel” of the materials they are using (fast or slow response, resilience, firmness etc) and the options they have available that may be the best “match” for you based on the information you provide them, any local testing you have done or mattresses you have slept on and liked or other mattresses you are considering that they are familiar with, and the “averages” of other customers that are similar to you. They will know more about “matching” their specific mattress designs and firmness levels to different body types, sleeping positions (side for you), and preferences (or to other mattresses that they are familiar with) than anyone else. Their recommendation of the “firm” version certainly wouldn’t be unreasonable based upon your mass and BMI.
Personally, I can certainly help with “how” to choose, as it’s not possible to make specific suggestions or recommendations for either a mattress, manufacturers/retailers, or combinations of materials or components because the first “rule” of mattress shopping is to always remember that you are the only one that can feel what you feel on a mattress and there are too many unknowns, variables, and personal preferences involved that are unique to each person to use a formula or for anyone to be able to predict or make a specific suggestion or recommendation about which mattress or combination of materials and components or which type of mattress would be the best “match” for you in terms of “comfort”, firmness, or PPP (Posture and alignment, Pressure relief, and your own Personal preferences) or how a mattress will “feel” to you or compare to another mattress based on specs (either yours or a mattress), sleeping positions, health conditions, or “theory at a distance” that can possibly be more reliable than your own careful testing (hopefully using the testing guidelines in step 4 of the tutorial) or your own personal sleeping experience (see mattress firmness/comfort levels in post #2 here).
I know you’re already deciding upon the BME, but I’m assuming that you’ve read the mattress shopping tutorial here but two of the most important links in the tutorial that I would especially make sure you’ve read are post #2 here which has more about the different ways to choose a suitable mattress (either locally or online) that is the best “match” for you in terms of “comfort”, firmness, and PPP that can help you assess and minimize the risks of making a choice that doesn’t turn out as well as you hoped for and post #13 here which has more about the most important parts of the “value” of a mattress purchase which can help you make more meaningful quality/value comparisons between mattresses in terms of suitability (how well you will sleep), durability (how long you will sleep well), and the overall value of a mattress compared to your other finalists based on all the parts of your personal value equation that are most important to you (including the price of course and the options you have available after a purchase if your choice doesn’t turn out as well as you hoped for).
While again nobody can speak to how any specific mattress will “feel” for someone else or whether it will be a good “match” in terms of comfort, firmness, and PPP because this is too subjective and relative to different body types, sleeping positions, and individual preferences, sensitivities, and circumstances and you are the only one that can feel what you feel on a mattress … outside of PPP (which is the most important part of “value”), the next most important part of the value of a mattress purchase is durability which is all about how long you will sleep well on a mattress. This is the part of your research that you can’t see or “feel” and assessing the durability and useful life of a mattress depends on knowing the specifics of its construction and the type and quality of the materials inside it regardless of the name of the manufacturer on the label or how a mattress feels in a showroom or when it is relatively new so I would always make sure that you find out information listed here so you can compare the quality of the materials and components to the durability guidelines here to make sure there are no 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 before making any purchase.
Many online mattresses have a very good trial period and return policy so you can try them in your bedroom instead of a showroom with little risk (outside of the time you spend sleeping on it and/or returning it if that becomes necessary or any costs involved in the return process) so if it’s not a “good enough” match for you in terms of comfort, firmness, and PPP you can just return it and try another mattress if your choice doesn’t turn out as well as you hoped for but once again you will only know whether it’s “good enough” to keep it and you won’t know whether it would have been better or worse or how it compares to other mattresses that you could have purchased instead that you haven’t actually tried in person.
I would focus upon your present situation and weight, and if you find the mattress to be a bit too firm a few years from now, you could always modify the surface comfort with a topper. But focusing on the “here and now” is always the best course of action, as you’ll be ordering this product to sleep upon it immediately. The BME does have a 120 night trial if you do find the product is too firm after trying it out for a few months.
As there is already some sinkage of the wire grid network, I would look at replacing this frame, as the mattress will have no choice but to contour to the surface upon which it is placed.
An all foam mattress will generally do best with a firm, flat, and evenly supportive support surface underneath it that has minimal to no flex under the mattress and for larger sizes with at least one center support beam that has good support to the floor to prevent any sagging in the middle of the mattress. The components need to be strong and durable and stable enough to support the weight of the mattress and the people sleeping on it without any of the parts bending, sagging, or breaking over time. The support surface under the mattress should have enough surface area to prevent the mattress from sagging through any gaps or spaces in the support surface over time but still allow some airflow under the mattress. I would suggest that in a slatted support system (either a foundation on a steel or wooden bedframe or a platform bed with a slatted support surface) that any gaps between the slats are no more than 3" (with 1 x 3 slats) although less than that would be better yet.
I wouldn’t use a wire grid foundation for an all latex mattress, and I’m still not necessarily a fan for long-term use with a foam mattress using a firm polyfoam core. It may be suitable with some modifications although it still wouldn’t be my first choice. You can see some of my comments about wire grid foundations in post #10 here and post #41 here. Additionally, most of them that I’ve seen also appear to have some percentage of customers that report squeaking issues that may be difficult to locate and solve although it may be possible to fix the squeak either by re-tightening any bolts or adding a washer or by lubricating any metal on metal contact points that are squeaking (including the angled braces).
Overall I think using a wire grid foundation as you described (albeit a stronger version) would make a reasonable lower budget choice for a mattress like the BME that has a firmer polyfoam base although as I mention is my previously linked posts it isn’t my first choice.
I look forward to hearing what you decide.
Phoenix