I would try a small independent one in a town house with a brass plate on the door (you know the sort of thing) - i'm looking for one now - in those establishments even the receptionist is highly skilled and will often do the fittings. They're all educated scientists. I wouldn't have any worry about that sort of optician.
Since transition began, I have used Specsavers, D&A ( Boots ) and an independant optician. By far, the independant was the best for professionalism from reception to fitting. Specsavers were the worst for me as they had great difficulty in dealing with deed poll/name change stuff as I used them as a male. Poorly trained chain store staff culture forced me to finish with them.
D&A are in the middle, in my town they are rather good but privacy within the store is almost non existent as it is within a large indoor shopping mall.
Find a good independant if you can, it may cost more but you get the great service you deserve