Recorstores helps a lot, about 100 stores in the city:
https://recordstores.love/FR/Paris
My usual expensive walk consists in going first in Châtelet/les Halles area in the very center (La Fnac, OCD Lescot, Libraire Gilda), then in Quartier Latin on the Left Bank (Gibert Joseph, Crocodisc, OCD les Ecoles, Crocojazz, Dame Blanche and Paris Jazz Corner).
Otherwise, a lot of shops in Eastern Bastille (Le Silence De La Rue, Souffle Continu for example) and a few not far for Barbès/Montmartre area (I quite like Balades Sonores).
During the weekend, there is also a flea market in Saint-Ouen in the North of Paris with a dozen of small record shops in and around one of the main buildings, but I have not been there in more than 5 years.
For new stuff, I higly recommend Gibert Joseph (also fantastic for new and second-hand DVDs). For jazz records Paris Jazz Corner and Crocojazz are highly recommended but are indeed very expensive.
As of October, Crocojazz is still open. However, everything (new or second hand) )is priced with a 20% discount for more than a year, so the best items from the shop are gone and I wonder if it does not indicate that the shop will close within a few months/years.