I'm not from the Windsor area you were recommended but I just used the snobe website to help me find schools in this area for 13+ and there are several mixed schools with lots of useful information, so perhaps try searching there.
There is also a UK government school search to help you find the nearest school to any particular address. Select the ‘Location’ option, and enter your address (or use an address nearby the place you hope to be living soon). You will receive a list of schools, starting with the closest. This will give you a list of all types of schools, as well as their address, their latest Ofsted rating (if eligible for inspection), and the approximate straight-line distance from your home to the school.
Use the tick boxes on the left of the page to select just primary schools, schools of a particular denomination or faith, single-sex or co-educational schools, or to exclude independent schools from your list. For families living near the border of a local authority, this is a particularly useful site, as it lists schools in all local authorities. You may find that the nearest school to your home may be a school managed by another local authority
You can also find a list of all state schools in any town in England by searching for the LEA (Local Education Authority). Every state school in England comes under the control of its area LEA. For example, I just googled 'Which LEA is Windsor in?' and quickly found this link to the LEA for Windsor . From there, I can see a list of all the state schools within a certain age range and lots of information about how to apply, the process etc .
Finally, while searching, I found a very useful Guide to in-year transfers in the Windsor area - specifically written for children who are moving into a new area and need to find a school.
I hope this helps - good luck!