Since I lived in Windsor and did not use a hotel, I cannot recommend one. What I can recommend is that you walk into Eton after your tour of the castle.
Eton College is ancient, majestic, and splendid to look at even just from the outside. The walk from the castle across the Thames past the masses of swans is delightful. Eton’s high street is filled with darling little shops, including old traditional clothiers where the students buy their uniforms, plus book shops, antique shops, etc.
Just as you get into Eton, to the left and down a few streets, is the Waterman’s Arms, a charming, very OLD, pub. https://www.watermans-eton.com/
On the right is Côte, which is part of a small chain, but also really a nice place for a late lunch. They have outdoor, riverside seating, which is pretty fab. https://www.cote.co.uk/restaurant/windsor
Enjoy!
Edit: you might also check out The Crown and Cushion Inn, in Eton. I’ve enjoyed a pint or two here in the pub, and the inn gets excellent reviews. https://via.eviivo.com/en-en/Google/crowncushionsl49af?startdate=2025-08-12&enddate=2025-08-13&adults1=2&children1=0¤cy=GBP&roomtypeid=6315&rateplanid=13069&fbl=true