Hello again. First let me say that I am not an expert and that anything I say is just my opinion and my experience. The sandals have a firm contoured footbed. They are touted as being orthopedically correct. For me, I had a short breaking in time and yes I have often worn them all day long. My husband is now breaking in a wide width with an extra high arch support and he thinks they will take a little longer for him to get used to. Given your history, it would probably be a good idea to ask your doctor.
Also, any retail store that I have seen Birkenstocks sold in, have had very well informed sales people with some training in foot health. It would probably also be a good idea to find a retail store and try them on. I think you will know very quickly if they are for you. As well, I would suggest looking at their website for information on their constuction. I agree that they are expensive, but many of the components can be repaired or replaced and mine seem to last a long time. This was long winded, but hope it helps.