There aren't many hotels In Paris with pools. The Ritz would be an exception, although IIRC it has a health club which allows people who aren't hotel guests to use the (indoor) pool. PH Vendome has a sort of soaking pool as part of its spa, but it's not a pool for swimming. To find pools near Paris, you essentially have to go at least as far as Versailles or Fontainebleau; I'd start with the list of R&C properties, perhaps in some of the smaller towns on the way to the Dijon and further south.