Cindy, since your question was posed in 2012, you may have moved to France and found a place to live. Where to live dépends on a lot of personal préférences like do you like winter, hot weather, etc. The summers even here in Le Centre where I live can get into the 90°Fs but in the South it can get hotter and for longer periods. Most French houses don't have AC so the heat can be oppressive. I live in a small village of 450 people half with older people and half are Young families. It's squeezed between two towns of reasonable size with very good shopping and Orléans is only a 10-15 minute drive to centre ville. We have good train connections to everywhere. Paris is only one hour away by train. We have the best health care facilities with the Regional hospital and two brand new hospital complexes in the South and north of Orléans. We landed in the Orléans by an accidental choice but are very happy we did and we are in what I call a Sweet Spot in terms of tranquility, convenience and availability of services. One thing to consider if you are getting up in age is the availability of emergency services like ambulances and hospitals with emergency department in case of a heart attack.
Houses with stairs may become a problem in the future but where we are there are few one level houses to be found. Maybe in other areas they are more prévalent.
I have no knowledge of assisted living places but there are some Maison de le Retraites around but I think these are for older people who need full time care, more than assisted living. We would call them nursing homes in the US. The costs vary depending on the facility and the care provided.