Perhaps I lost track of your question but ...

> they confirmed that we will be able to take our luggage to the upper deck!

Of course you are allowed to do so. I never thought it was your question. I thought you wanted to avoid carrying your heavy luggage upstairs. There are luggage racks at both levels. Also you wrote (dindn't you?) you had sent e-mail to SNCF to ask if you could change seats (not about the luggage).

hi kappa,

yes, i did write to SNCF to ask them if we could change seats ... and i also told them that i was concerned about being separated from my luggage. so they wrote back saying that i can't change seats but i can bring luggage up to the second deck so i won't be separated from my bags.

thanks!!