A good place to go to on how the Brits organised their tanks in '44-45 is at:
http://www.bayonetstrength.150m.com/Arm ... giment.htm
I also go by the Army lists in the back of an old set of Firefly rules by Tabletop games, which I've found to be remarkably accurate even if they are old.
In there they state that there were numerous organisations at the Squadron (Company) level, but that from June 44 there were 4 platoons of 4 tanks each, each Platoon comprising 1 Firefly and 3 75mm Shermans, with a Squadron HQ of 4 tanks, making 20 in total. The 75mm Shermans were M4A4s from photos that I have seen from Epsom and Goodwood, or UK65s.
Sometimes the Squadrons were organised as 5 platoons of 3, with each platoon having 1 Firefly and 2 75mm Shermans, plus HQ section of 4.
And sometimes all the Fireflies were put into one platoon, the reason being that the Fireflies were usually the first to be shot at by German tanks.
The Guards Divisions were nominally kept at or over strength, so vary the mix of Fireflies to 75mm.
As Fireflies became more common so the mix of Firefly to 75mm was evened out a bit. I think by Sept '44 the mix was 50/50.
As for Shermans with skirts, I think they were used mainly in North Africa and Italy. So you can still use the UK16s. I think some were also used in Europe, and I tend to use the ones I have in HQ sections.
Whatever, they're Shermans with 75mm guns and so they're all about the same anyway.
Hope this helps,
Battler