Every Orthodox service I've been to we stood the entire time, though I never went on special holidays. My inner ex-Catholic wondered is it really church if I don't kneel and stand, kneel and stand, kneel and stand all through the service?

My Ukrainian ex had a worship space in a corner. It didn't have any rugs but had hauntingly beautiful hand painted icons. Maybe rugs are more of a thing in the old countries?

Practices in Orthodox services can differ. For example, in some Romanian parishes everyone has knelt while the Gospel was being read, but I have never seen this elsewhere. And as the other poster mentions, full prostrations are done (and widely across the Orthodox world) in certain contexts.

Some churches in Greece and Albania have pews -- the concept was brought back from the North American diaspora where Orthodox parishes were set up in former Protestant or Catholic church buildings -- so you can do all the standing, sitting, and kneeling you might be accustomed too.

Churches probably have some kind of theological explanation, but alternately kneeling, sitting, and standing is much better physiologically. Having a large and diverse group of people all stay in the same position for an extended period is very rough on their bodies, and some more than others. Periodically switching prevents injuries caused by maintaining too much static load for too long in any one place. Probably also helps keep everyone awake. For the same reasons it's a good idea to occasionally switch positions while working.