Get a saddler who has been reccommended, either by peeps on here or by friends/other owners at the yard. The saddler should come with a wide range of saddles to suit your needs and budget.
I would be interested too as I am not far from you and need to arrange a first fitting.
Ingatestone saddlery have saddle fitters but I don't know how much they charge and I don't know anyone that has used them, so it would be good to see who uses saddlers in Essex here for recommendations!
I don't know if this is any help but I cover Essex and will flock many types/brands of leather saddles. I fit for www.nativeponysaddles.com and we have Phoenix saddles for the less wide and flat .