There are a few Mr Men books for the Christmas season- Mr Christmas lives at 1 pole and Lil Miss Christmas lives at the other pole (I can’t remember which is which - but I seem to recall a flying teapot), and there are a few more Mr Men versions of pantomime type ones too.
Thomas the Tank Engine also helps out Santa in 1 edition.
We have an Usborne book of 3 stories of Christmas (1 has an elf creating a machine to make toys and they all start to turn out the same).
The ones that there is a duck on every page - publisher - we have a couple of wintery ones from them. Sheep getting lost on a hillside type of thing.
A couple of Christmas and winter anthologies- collections of poems, songs, short stories and extracts from longer books (like Santa appearing in Narnia) all together.
If you go to a good bookshop from October onwards, maybe more into November, there will likely be a table of seasonal offerings. I built my collection over a good few years, mostly bookshops but the odd few from school fair book stalls and charity shops, and a few presents DD got from others also. That way it’s nice to have a few smaller baby books that are favorites coming out again while having something newer and more geared to their current age to enjoy too.