Hi icebladexi, and welcome to the Mattress Underground 
Any mattress you finally choose will be based on your Stats (height, BMI, sleeping position(s) and any underlying health
Conditions) and your PPP (Posture and alignment, Pressure relief, and Personal preferences).
A DIY mattress project can be the most rewarding, as you can zero in on the exact comfort and support levels you prefer…but it can also be highly frustrating as there may be a good deal of trial and error in finding the right firmness and density.
Unfortunately there is no real ‘list’ of ILDs for particular body profiles…a mattress is a highly subjective purchase; 2 people of the same Stats can have wildly different opinions on what feels most comfortable for them.
In general, you can see by comparing the the Mattress Specifications You Need To Know to the Mattress Durability Guidelines, how durable specific materials are; latex is one of the most durable mattress materials you can have. Also Talalay and Dunlop latex rubber have very different ‘feels’ with Talalay being ‘bouncier’, while Dunlop is more dense (the usual comparison is between angel food cake and pound cake). For foams, We suggest any foam in a potential mattress has no more than an inch or so of lower grade foams (for memory foam no lower than 4 lbs/cuft for normal range weights, and 5lbs/cuft for higher range weights) and if polyfoam is used, with at least 1.8 lbs/cuft density, just to ensure you have support.
As a higher BMI sleeper, you need to make sure whatever you use for a top comfort layer is not too soft or too thin, as this can allow you to ‘bottom out’ on the firmer layers below. Which can affect alignment as well as cause ages and painsYou might want to read what @Phoenix has to say on layers here. A ‘transition layer’ acts as a gradual increase in firmness between your comfort and support layers. It’s largely a matter of your Stats and sleep profile-
A mattress of medium firm comfort layer and firm base would not have specific transition layer, for example. Higher BMI sleepers need a thicker, firmer mattress than lower BMI sleepers; in your case the topper may be a perfect solution to add a little plushness without affecting your alignment. A 9" mattress would be the minimum for your body profile, and you may want to add a little height.
This is the sometimes frustrating aspect of DIY, drilling down to the exact comfort and support levels you need. Patience and consideration is the key to a successful DIY, and if you get stuck, you may want to contact one of the DIY experts among the Trusted Members of the site, like APM, who have many years of experience in assisting with DIY projects and can possibly advise you on specific questions on layers suitable for your body profile. Keep at it, don’t get frustrated, and please let us know how your build is going!
~ Basilio