Any paperwork?

from your question I’m assuming you don’t have Residencia, so my answer is based on that:

When you say “for the winter”, I presume you mean the maximum 90 days allowed for a non-EU citizen, which as a British National is what you’ll be as from 1/1/21?

As it’s a holiday, you shouldn’t need to register on the Padrón so all you are going to need is your passport, some kind of health / travel insurance (EHIC Card no longer valid as from 1/1/21) and of course if you intend to drive an International Driving Permit to accompany your UK licence which I understand is available from the Post Office.

Yes, still very much open.  Social distancing and masks whilst outside at all times is now part of normal daily life, but we’re getting on with the new “normal”

Ah. This is where I have the problem

I want to stay more than 90 days but not as much as 183

Surely there must be a way of doing this?

Short answer - Nope.  There is no such thing as a long stay tourist visa.  You either take the 90 days, or apply to migrate - those are your two options as from 1/1/21

And again, as from 1/1/21 you have to stay a LOT longer than 183 days to maintain your visa - after that date, to keep the visa, you may not spend any longer than 10 months aggregate in your first five years outside Spain ...

So many people seem to have forgotten that Brexit made a difference. We left the club, we left the EU, we are not 'one of them' anymore. But Brexit voters surely knew what they were voting for? A maximum of 90 days in any 180 days period as visitors/tourists. Or maybe not!

Chris