Hi dn and yianni54,
[quote]I’ve only heard of Vi-Spring, from another forum member. www.vispring.com
A look at their website tells me they’re likely in the premium range too. [/quote]
VI Springs would generally be considered in the “ultra premium” range. One of the members here Brickell Mattress / Select Foam sells them and they would be happy to tell you more about them … just be prepared for some serious sticker shock 
Some other similar innerspring / natural fiber mattresses are mentioned in post #2 here.
You can also read some of my thoughts about more premium mattresses in post #2 here and post #2 here.
A few other ultra premium brands are mentioned in post #14 here but these are not mattress that I would suggest buying without extensive personal testing and consultations.
Phoenix