I forgot to post back here, but in the end I just dropped into BC and picked up a Specialized Tactic II (in fluoro green for bonus nodderness). It seems to be fine as a basic all-rounder, confusingly little to adjust - only chinstrap length and a single dial at the back, but seems to fit and is easy to loosen and adjust each time I put it on, which is a bit of a revelation for me. Makes a big difference to how comfortable it is.
I forgot to post back here, but in the end I just dropped into BC and picked up a Specialized Tactic II (in fluoro green for bonus nodderness). It seems to be fine as a basic all-rounder, confusingly little to adjust - only chinstrap length and a single dial at the back, but seems to fit and is easy to loosen and adjust each time I put it on, which is a bit of a revelation for me. Makes a big difference to how comfortable it is.