Hi TwistedRoad,
The 3" topper on a Nature would certainly be softer than what you have now (the topper would be @ 15 ILD if it was the Active Fusion) but depending on the type of latex in the Savvy Rest you tried it would be closer to what you are currently sleeping on (at least in the top layers) so I’m not sure why your wife is feeling it as being softer.
They don’t make the slow response any more so it would have been the fast response and if it was the Active Fusion then it would have been 15 ILD.
The better sources for latex toppers I’m aware of are listed in the component post here and if you are interested in LI Talalay then both SLAB and KTT sell the complete range although KTT has lower prices.
Phoenix