Hi Connor,
There is no way to know this for certain because it will depend on the conditions of use, what the mattress is exposed to, and on when the gradual loss of comfort and support leads to crossing the thresholds from sleeping well on a mattress to “sleeping OK” to “tolerating it” to finally deciding to replace it. This will be different for different people.
You can see some of the results that different covers can have on latex in post #3 here and in post #3 here.
There is also more in post #2 here about the factors that can oxidize or break down latex.
Having said all that … I think that in most “normal use” conditions where the latex isn’t exposed to substances that can break it down prematurely that it should last for at least 5 years with only minimal covering but beyond that there would be too many variables involved to be able to guess.
If you are designing and building your own mattress out of separate components the first place I would start is by reading option 3 in post #15 here and the posts it links to so that you can make sure that you have 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. 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).
There are too many unknowns, variables, and personal preferences involved to be able to reliably predict whether any design will work well for any specific person based on specs (either yours or a mattress) or “theory at a distance” (see mattress firmness/comfort levels in post #2 here). The only way to know whether any combination of layers will work well for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) will be based on your own personal testing and experience. Thinner mattresses are generally firmer so if you are a back or stomach sleeper and don’t sleep on your side or if you tend to prefer firmer mattresses then the odds of success with a thinner mattress would be a little higher but side sleepers will often need some softer layers on top of the firmer support core so they may prefer a combination of layers that ends up being a little thicker. There is more about the effects of thickness in post #14 here.
The component post I linked earlier includes the better sources for covers I’m aware of and post #4 here includes a list of the thinner more stretchy knit covers I know of from the list.
Phoenix