Wow, a modular mattress system.  Has anyone seen / used / investigated / priced Sterling Sleep Systems upgradeable mattresses?   They unzip so you can install parts.  I didn't find anything with the Search here.

http://www.sterlingsleephospitality.com/technology.htm

They have a "tempered" Marshall coil, apparently from Leggett & Platt.    I'll have to read through all the details.

 

Leggett & Platt coils, choice of Marshall,   660 coil Lura-Flex, or 342 Bonnell.   Foams and covers are user-replacable.  Doesn't say whether springs are.

660 Lura-Flex (open end offset coil)  would be kind of low-end for a Lura-Flex, maybe?  Sounds like maybe these are overpriced and you could get an upholsterer to make you a zipper cover and "roll your own" based on something purchased locally.

We have debated before why someone has not done this for innersprings.  It is an interesting idea, but I would like to see some with a bit higher quality material on the innersprings (latex, wool, cotton, maybe 5lb memory foam, and no PU foam).