The one thing that helped me the most was to stop using my Ottoman and sit with both feet flat on the floor. I don’t remember where I got that info, but it works for me.
I work part-time in quasi-retirement. Most of it is at home, so I stand up at least half of that time at my standup desk. And I try to walk a mile around the neighborhood everyday. If it's a day I go to the office and I have to be there all day, then I have to sit down at a desk and find myself more tired when I come home than the days I stand up a lot.