My sister and I will be traveling from London to Windsor, then on to Oxford for an overnight stay. We would like to have our luggage sent ahead to the hotel in Oxford from our hotel in London. Any suggestions?
Have you considered just leaving your luggage at Windsor train station while you're there? Once you're done exploring, you can just pick it up and travel on to Oxford. It's relatively easy to do and there are several left luggage places at or near the station, I believe. It would be much less expensive and less risky than trying to find a place that will send your luggage ahead.
There are a few established companies that do luggage transfer but most deliver the following day after collection. Same day delivery may be possible but could be much more expensive.