Sitting in a wheelchair is guaranteed to leave you with horribly swollen feet. As Brian said, the key is raising your feet. I do a tiny amount of walking (like a few metres a few times a day) but that means I can sit on my (raised) settee with my feet up on the seat of the walker. That helps. Plus, I always lay on the bed in the afternoon for a couple of hours. Sometimes I fall asleep, but mostly don’t, that just allows me to get my feet level with my body.
Anytime I’m unable to move off the wheelchair for hours leaves my feet bright red, swollen and mottled.
In hot weather this is sometimes not enough. Even now, I have my feet up on the walker seat and can see that one foot is swollen.