Hi Tamsin,
Not a silly question at all.
We have a wool filled duvet (from UK) it has no tog, it changes as you require. Really very good. There is sometimes a need for an extra throw over the top, but this is only on very cold nights.
I'd get a summer weight, say 4.5 and have a throw ready if you need it.
Last winter, pre heating and insulation, we had 2 quilt nights!
I have found bedding a tab more expensive here. You have to shop around.
Regards, Febe