Fred, as you know I have the same problem!
Most manufacturers don't give a weight rating for their chairs, they used to upto 16/18/20/22 ST.
Of the chairs recommended a couple have weight ratings upto 114KG (17.5 ST) nowhere near strong enough for me or you.
I have a few chairs,
A fox roamer (18)
A chub (22) and another one all have done really well over the years but now well past their sell by date and well battered and very heavy.
I also acquired a Fox adjusta level a couple of years ago, (johno has done a bit off work on it strengthened the sides as I was bending them all the time) and it seems ok now, not the comfiest in the world but very very light.
Lets see how we get on, had a look in Chapmans the other week but as I said none of the major manufacturers give ratings now.So Chapmans wont cover our weight range.