Interesting question as there are so many different approaches to this and they all have merits in different ways. Does a welcome box work for a one year old? I really don't know the answer.
We bought a cuddly toy (which was given when we did intros) and made an age appropriate, tactile book for each of the children (which went to the Foster Carers a week or so before intros started) - the cuddly toy was the narrator for AD's book and was in most of the pictures; not for AS's, though, as I thought that it might freak him out a bit - not sure that I was right on this but hindsight is a wonderful thing).
AD was much older when she came to us (age 5) and looked at the book quite a lot in the early days, and I've seen her peeking at it more recently too (she is now aged 16). AD also came with a album of photos of her early life from the Foster Carers and she tore up nearly all of the photos - significant, perhaps? I had a series of photos taken of the children by a professional photographer for DH's significant birthday year before last and AD's cuddly toy appears in many of them (children got to choose what was in or out of the photos). Go figure!
AS was still little (20 months) and hardly looked at the book at all but latched on to the cuddly toy which became his constant companion for years (he is now 9 and the little leopard is still a favourite, although the bunny family seem to have surpassed the little leopard - yes AS still loves his cuddly toys!).
What I will say, though, is that both children have re-visited the books that we made for them (with pictures of the house, the cats, the surrounding area and us) endlessly over the years of their growing up. I often find AS's book in his bed when I tuck him up and it feels special that he likes to look at it. So, what I'm chucking out there is the suggestion that this exercise isn't a one-off "welcome" thing but something much stronger and bolder than that in "claiming" your child.
It was suggested to us that we should switch our brand of washing liquid to whatever the Foster Carer was using. Why am I mentioning this? Well, you may find that at that young age they will arrive with a blanket and may reject the one that you offer as it doesn't smell right. So, not saying don't do it but perhaps think a bit around how it might be introduced. Both children have been bought special blankets here but that was over time.
I suspect that a one year old will try to eat a book (hardback or otherwise) or laminated pictures. The book will probably be at least partially digestible - doesn't mean don't do it but you might want to keep it safe if you want it to be something for them to re-visit. Or let them eat it if you don't mind either way once it has been read. The laminate may give them tummy ache, big time, so perhaps think about this too.
I didn't do a welcome box but do have a memory box for each of the children containing things that have been important to them (in their time with us and before) to help with life story work but also to give their early lives some context. Both children know that the boxes exist. Both have probably peeked into them (although no evidence of this!) but I will hand them over, with context, when the time feels right.
So, long story short, I don't think that I have answered your question at all. Sorry!