Hi drew904,
Welcome to the Mattress Forum! 
I wouldn’t be able to determine that via an online forum, as there are too many individual unknowns, variables, and personal preferences involved in choosing a mattress for someone else to make specific suggestions based on specs (either yours or a mattress) or theory at a distance that can possible be more accurate than your own careful and objective testing (using the testing guidelines in the tutorial post) which is always the most reliable way to predict which mattress will be the best match for you in terms of PPP (Posture and alignment, Pressure relief, and your Personal preferences - see mattress firmness/comfort levels in post #2 here).
The OSO uses a 1.5" layer of plush 14-16 ILD blended Talalay in the uppermost layer, but this works in unison with the 1.5" of 2 lb polyfoam beneath that to form the upper “comfort layers”. Rotating the mattress to have the DreamCells under your shoulder region will allow for even a bit more plushness as well, but I unfortunately wouldn’t be able to predict if this combination will be “too soft” for your personal preference.
Again, I wouldn’t be able to predict the level of comfort that you might find “comforting”. The Luma Hybrid does allow for a zoned innerspring unit that is more supportive that you may desire to select (I’d suggest a phone conversation with them to determine if this would indeed be their recommendation), so I don’t think that support would be an issue for you. As you’re aware, with the Luma Sleep System you do have the ability to choose the firmness of the latex layer within the hybrid mattress, as well as choosing different ILDs of the 3" topper, and they can be assistive in selecting what they think might work best for your BMI.
It is true that with a higher BMI there are some unique challenges, and in general you’d want to consider firmer layers (especially within the support layer), and you may desire thicker and slightly firmer comfort layers as well. Post #3 here has more information and suggestions about higher BMIs that is worth reading.
Both OSO and Luma Sleep are members of this site which means that I think very 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.
Of course you can’t feel quality or durability when lying down atop a mattress, so you need to make sure that you find out the 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. Southerland doesn’t list complete specifications of the Rhapsody on their web site, and JaxMattress has no meaningful information on their site as well about this mattress. If you’re able to find out the componentry within this mattress, feel free to post it back here in this thread and I’ll be happy to comment upon it.
Phoenix