idk, i think that thin mattresses have been a fixture of houses of most of the societies of people with genetic predisposition to higher joint flexibility (ie, asians)

my experience is that it's actually circulatory problems that cause discomfort from more rigid bedding, nothing to do with joints

your tissue is compressed where in contact with the mattress so if your circulation is impaired you are more likely to get problems with hypoxia and slow waste elimination (and yes exercise also helps there because it empties out the lymph nodes) 

 a firm matras does sound like the happiest medium then imo considering both joint support + decompression 

 wat a thermorest?  

 https://www.atmosphere.ca/en/all-brands/therm-a-rest.html 

 i can imagine if that's what uve been accustomed too it the best