Hello everyone 
I've been shopping for a new mattress recently.
I wanted one chemical or plant based fire retardant treatments. It seems unnecessary to use chemicals because, according to these retailers, that you can achieve sufficient fire retardancy with wool blends and graphite latex layers.
These are the retailers I found. I hope they are of use to those of you who are interested! 
I have zero affiliation with these companies; I don't know if they're even any good, so please practice your own due diligence!
business
type
price
product name
latexsense.co.uk
latex
£554
Latex Coir
unamattress.co.uk
latex
£675
Essential
naturalmat.co.uk
spring
£700
Splendid
elymattress.com
spring
£790
Ely
thewoolroom.com
spring
£799
herwick
cottonsafenaturalmattress.co.uk
spring
£814
Appledore
naturalsleep.co.uk
latex
£839
Natural Nb4
milammattress.co.uk
latex
£889
milam
greenwoodsfurniture.co.uk
spring
£1,095
burgessbeds organic 1000
abacaorganic.co.uk
spring
£1,095