Hi dbergan,
Welcome to the site and it’s great to see that you’ve already read the tutorial 
[quote]I’m intrigued by latex, but don’t know offhand where to try them out in my area of the US. The only mattress factory I know of in town is Comfort King… but they aren’t members here. (Do you know anything about them?)
Where should I start?[/quote]
The better options or possibilities I’m aware of in the Sioux Falls area (subject to making sure that any mattress you are considering meet the quality/value guidelines here) are listed in posts #2 and #3 here.
I don’t think any of the manufacturers or retailers there have any all latex mattresses (although some use latex in the comfort layers) so if you are interested in testing “all latex” mattresses you may need to take a drive to either Omaha/Lincoln or to Minneapolis/St Paul.
Phoenix