Standing isn’t an answer to sitting, neither would be leaning. Sedentary is sedentary. The best option is just to stay as active as possible. I switched to a standing desk about a year ago and have tried many different setups. Pure standing became hard to manage over long periods of time, and a leaning stool ended up causing me knee pain. I have finally settled on a home-made multi tiered box setup that offers me a number of positions to use while working. I can go one leg at a time into deep hip flexion, I can do either leg in pigeon, i can reverse ballerina, I can even step up on to the top and sit in the bottom of my squat at my standing desk. I can even just sit, but since it’s made of wood it isn’t comfortable enough to sit for too long which forces me to change it up. This is the best option so far that I have found and it allows me to actually get more mobile while working. Hope this helps.

I would love to see a picture of this box setup