I think your "missing the FD, but not the stress" captures it exactly. You're FI, RE and you CAN DO WHAT YOU WANT! (Including volunteering or working PT in some FD role if that floats your boat.)
I found "retirement" somewhat different from what I expected, but more for the better than the worse. My wife took an overseas job in Asia about 5 years ago and I took (slightly) early retirement at 62. After 4 or 5 months living in Manila, though, I was getting bored. My wife had a great "package" and I had a couple of pensions, so I really didn't need to work, but when I was offered a job as a "senior advisor" working 3 days a week but able to take off nearly whenever I wanted, I grabbed it. So, I was able to accompany my wife on most of her business trips and travel extensively as a tourist throughout Asia during the four years we spend overseas. Wonderful!
We returned home a little over a year ago and my wife (8 years younger) decided to take a year or two "sabbatical" to finish a graduate degree. At this point she was also getting a nice pension and we have substantial investments and savings, so again I didn't really need to work, but after about 9 months of traveling (skiing in Hokkaido and BC, schmoozing for 2 months in Charleston, etc.) and resettling in DC, I was again getting a little bored. But, again, I was offered another "senior advisor" position guaranteeing me about 100 days of work a year, but letting me take off nearly whenever I wanted... So in the past 9 months, I've since spent a couple of weeks skiing in Park City, a couple of months in Patagonia, a month in Charleston, etc. Mostly my wife accompanied (except the ski trip), since with the internet she can work on her dissertation nearly wherever she wants.
I do think I may slow down more with regard to work in another year or so. Maybe teach a college course or two (I started as a college professor and kept teaching off and on throughout my career). Or follow my wife, if she decides to work again herself.
We'll see. But I will say, "retirement" has been a great adventure thus far; but rather different than I expected....
Good luck!