Hey there DIY123. Welcome to the Mattress UnderGround, we are glad you are here and thank you for the question.
I guess we do which that building a mattress on you own was as easy and DIY123, right?
Looking at what you’ve put together, this is what I see: the overall concept makes sense, but there are a few things worth thinking through before ordering everything. A DIY mattress is more than just throwing a few layers of latex on top of some coils and putting a cover around it. The transition layer, the coil/support unit, edge support, base layer, the stretch of the cover, and the FR/fire-barrier system can all affect how the finished mattress performs and feels.
With the difference in your weights, it is wise to consider taking advantage of the split and tune the upper layers independently. I’d probably look at 8" pocket coils, around 3" of medium Dunlop (roughly 28–32 ILD) as the transition layer, and then a split 3" Talalay comfort layer. For your 140-lb side, something around 19 ILD seems like a reasonable starting point, while for your wife at 200 lbs I’d probably be looking more toward 24–28 ILD. I’d lean toward 3" of transition latex rather than 2" to give a little more separation between the softer Talalay and the coils.
One thing to keep in mind with latex is that ILD doesn’t represent the entire story. Latex can be quite buoyant and has more pushback than many people are accustomed to with conventional foam. Unless you have had a latex mattress in the past. It can also feel firmer or more supportive than a similarly rated HD/polyfoam layer, particularly when you’re talking about a heavier sleeper compressing the material. So I wouldn’t get too hung up on finding the “perfect” ILD from the numbers alone. The combination of the layers and how deeply each sleeper engages them is going to matter. Also, with your wife being pregnant, I’d also consider a full-length body pillow or even a king-size pillow positioned to support the belly and legs. Besides providing comfort, that can help stabilize the torso and pelvis while side sleeping and reduce the tendency for the body to twist out of alignment. I would think of the pillow as another component working together with the mattress: the mattress provides the underlying support and pressure relief, while the pillow helps with positional stability. I love using a pillow to rest my arm on when sleeping on my side and if my wife is sleeping on her side at the time, it allows us to “hold hands” keep our hips from rolling too much, and keeps our arms and shoulder from rolling and straining.
For the coils, Texas Pocket Springs QuadCoils are one option I’d look at, although there are certainly other good choices. I’d keep the coil unit the same on both sides and do most of the tuning with the latex layers. I’d also pay attention to how the edge support is handled, particularly with a split king, and think through the FR/fire-barrier requirements and how that will be incorporated into the cover rather than treating the cover as an afterthought. Many folks build a mattress and throw a cheap cover on it, just to get it done. The cover can have a profound affect on the final feel of the mattress. How taut or stretchy can play a roll as to how the latex layers will expand or stay more supporting.
The nice thing about doing it this way is that you can change just the upper layer if one side ends up too firm or too soft. I’d definitely let some of the DIY latex folks here weigh in on the exact ILDs, coil choice, and construction details before ordering, but I think this gives you a reasonable starting point and, more importantly, leaves you some room to fine-tune the two sides independently.
Hope this helps and look forward to some of the latex DIY expert Trusted Members chime in.
Maverick