I do not buy usual souvenirs. I have done it when young and trow all away. The only thinks I kept where books, photo albums, decoration items with some local feeling.
In Paris I always go to Mona Lisait, a great bookshop, not the best, but maybe my best choice for albums at cheap prices.
Check their website for addresses and offers https://monalisait.fr/
I go also to Taschen library but I rather prefer the one in Brussels.
Enjoy shopping for books. It’s more fun and lasts forever.