Hi rbe.
Welcome to our Mattress Forum. 
Sorry to hear of the foam breakdowns on your Serta after only 4 years of use, and that the Purple ultimately was too firm for your needs. A DIY can be a great solution for salvaging some of the mattress components in good working condition (and turning it into something exceptional!) As what you’re doing is creating a DIY mattress out of separate components that are purchased from one or several different sources, I would refer you to Post 15 ~ DIY mattress design and choosing layers on your own and the posts it links to (and option #1 and #2 as well) so that you have more realistic expectations and that you are comfortable with the learning curve, uncertainty, trial and error, or in some cases the higher costs that may be involved in the DIY process. While it can certainly be a rewarding project … the best approach to a DIY mattress is a “spirit of adventure” where what you learn and the satisfaction that comes from the process itself is more important than any cost savings you may realize (which may or may not happen).
Deciding on latex firmness/thickness is a pretty multi-faceted process. I’ll get to that below
Generally, the thickness of a mattress is only one of many variables that can affect the feel and performance of a mattress but in higher weight ranges (or a higher BMI) the odds are higher that you may do better with a mattress that is thicker than lower weight ranges or a lower BMI (see post #14 here for more about the effect of thickness) but even this depends more on the specific design and combination of materials in the mattress and on how well your testing or personal experience indicates the mattress “as a whole” matches your specific needs and preferences in terms of PPP than it does on just the thickness itself. It will also depend on your body type and sleeping positions as well because side sleepers may need more softness and contouring than back or side sleepers.
The innerspring is rarely the weak link in a mattress so it doesn’t surprise me that only the materials in the comfort layer are experiencing a breakdown after only four years of use. It’s encouraging to have environmentally aware people on the forum looking into creative solutions to reuse mattress components. … Some repurposing ideas include pet beds, seat cushions for patio furniture, beam bags, pillow for neck support, under the knee or body pillow to relieve pressure on the knees and hips, draft stoppers, noise reduction studio padding, wall insulation (providing that there is no humidity), toy stuffing, nursery flooring, car seat pads, cushion stuffing, garden knee pad, Halloween costumes. I even heard of compost pile covering. If time does not permit to take on yet another project then finding a recycling center in your area that has a foam shredder machine may be a good way to go.
This is a stabilizing layer for the coils and coil perimeter padding, so yes I would agree with you to “leave it in place” if a short inspection shows it to be in still in good enough condition.
[quote]Stats for choosing firmness:
- I am ~110lb side sleeper. I like to feel enveloped by my bed, but am worried about lack of support as I age. I understand “soft” doesn’t necessarily mean “lack of support” but I’m worried anyway. I am willing to accept something flatter-feeling after some time with Purple got me accustomed to it.
- Husband is ~200lb and sleeps in various positions, but mostly back. He likes a fairly firm bed and is fine with the Purple Original. He basically told me to get whatever works for me, but he doesn’t like something overly soft.[/quote]
You did not mention your height and your partner’s to calculate your BMI, but thank you for sharing the other stats! Knowing this would make it easier to give any guidance and also to make sure that whatever you select meets the mattress durability guidelines here for your specific BMI. Even though you’d prefer not to do a side by side split because of “buyer’s remorse” with regards to your side, and also because you’re worried about a gap … here is just something to consider.
A split left/right configuration would certainly have the best odds of success in meeting both partners comfort and support needs. The mattress can be built so that the total thickness of the mattress is the same for each side, which means that there would be no difference in elevation, and with a suitable tight fitted quilted cover, the “split” transition area between sides is usually unnoticeable for most people. You can read more here about side by side layering in post #2…and, if you ultimately decided you liked your husband’s side of the bed better…you could reopen the mattress and replace the layers.
Depending on your BMI and a few other factors it may just as well be that with your willingness to give up a little of the side sleeping comfort cradle (now that you got used with a firmer surface :)) you may be able to “bridge the gap” between a large partner weight differential and get layering that would be a good fit for both you and your husband. He would need thicker firmer layers so that his spine is
"idk what I’m doing “can be a recipe for disaster especially when it comes to a DIY …. . A 3” latex is a perfectly good thickness to start with – very common for comfort layers but selecting the adequate latex ILD (firmness) plays an important role in the comfort/support equation and it should be based on your body weight, shape, weight distribution, and preferences.
The lower ILD … the softer the latex is. ILD can range from 14 (very soft) to 44 (very firm). Many of our Trusted Members have 3" latex layers for DIY projects and they are all extremely knowledgeable. They would also be able to help you make a decision based on your stats and comfort preferences. As mattress testing is not something, you’re currently able to do, the next best thing is to have a detailed phone conversation with a knowledgeable and experienced retailer/manufacture that have your best interests at heart. They can help “talk you through” the specifics of their mattresses and the properties and “feel” of the materials they are using. When choosing something online, it’s important to deal with experienced, educated, and helpful manufacturers who have the knowledge to guide you through the DIY process and find something that they honestly think will fit your specific sleeping positions, somatotype, BMI, and individual needs.
On top of my head, I’d recommend you reach out to DIY Natural Bedding or Arizona Premium trusted members to get advice on what has the chances to work best for both you and your husband. But you may want to peruse through our Trusted Member directory I linked above for more options
3’ gap between slats is quite adequate for your type of DIY. The thing you most want to consider is whether the wooden slat foundation has a good center support and it does not bend under the weight of the mattress and the people sleeping on it.
Hopefully, this is a good start-up on your DIY journey. Please keep us posted with updates.
Phoenix