We’ve sailed about a dozen westbound trans-Atlantics - all in October or November, some 7 day crossings from Southampton to New York, the rest longer ones from Mediterranean ports to Florida - and one to Texas. The Atlantic keeps its summer warmth well into November, so a good part of your itinerary should be in 70+ degree F seawater plus whatever air temps - probably well into the 70’s after the first couple of days.
Depends on route - will your ship call at any continental ports before crossing, and will you hit any Atlantic islands (all of which should have warmish weather that time of year)? - you should have “deck-sitting weather” much of the way. Of course, there is the outside chance of a hurricane necessitating course adjustment. If you sail south first, say to Lisbon or Cadiz before heading west you chances of warm weather most of the way increases.