Thank you @FLClover,
It's good to know other people have similar symptoms, so maybe not early dementia. Has your brain fog cleared now you are off them? I hope so. I already wear knee supports and wrist supports for doing my knitting but they get in the way much of the day (when cleaning, baking, etc). I have now added ankle supports.
I think I will ask my oncologist if I can try another AI but as you say they all have different side effects, but maybe others may be more bearable than on Letrozole. My GP has said giving up was not and option but my oncologist seemed to be of the opinion that as it was so small (to me it was still Cancer, no matter how small !) I could do without AIs as the risk of recurence was so small. I was quite surprised when he said that. I don't want any recurrence ! :/