My only other advice would be to get on the phone.
I did this when we booked somewhere, admittedly in Leeds, where they only did rooms for 4. I said we weren't interested in booking unless we could all share a room and they sorted it very quickly I have three young children but they're all too big for cots.
Look on kijiji or gumtree or craigslist for apartments for rent by owners. They are much cheaper than hotels and you will get much more space for your money. I have done this in various places in Italy with great luck.
we stayed here recently http://www.parisriverside.fr/en/ with 4 adults and 2 small children - it was fantastic - the owners couldn't have been more helpful. Although it isn't IN central paris it was realy easy to get into the center on the RER and actually it was nice to be outside Paris some of the time for a break. We were there 3 days and I would highly recommend with children!