When I first moved to the USA in 1990, as you say, every day was shirt and tie and real trousers -- except for casual Fridays when you could get by without a tie (I think the wearing of jeans came later -- certainly no shorts).
At that time --24 years ago now -- I don't think anyone wore shorts in England (excepting very young kids) -- maybe at the beach -- I don't recall. I know my friends were surprised the first time I went back wearing shorts.
Now, like you, I work in my own office (I don't work from home -- I have the Pleasure Dome) -- in the summer I wear shorts and Hawaiian shirts and sandles (I go barefoot in the Plaesure Dome) -- in the winter I wear jeans and Hawaiian shirts and sneakers.
The other nice thing about working at home is my short commute down one flight of stairs. I was reminded of that today as I headed to the Mathworks. I figured 20 minutes, allowed for 30, but it took 40. And, that was a reverse commute. The traffic heading into Boston was far worse.