I'm not vastly experienced but am currently unwillingly rearing indoor pigs.
They are completely happy as far as I can tell on cement with oodles of space and a whole round bale of hay (it just happened that way

) to pull about and rummage in. They see lots of people and other animals as they are in a large pen (actually it's the bull pen - just as well we haven't bought a new bull yet!) in the corner of the cubicle shed where the cattle are wintered; the collies and hound pup run in and out, we're in and out. They get the odd walk or even afternoon out if the weather and ground are suitable, but frankly they were cold and shivering outside (even with a toasty cosy bedroom) and have been warm, dry and apparently perfectly happy ever since I brought them in "for a few days" several weeks ago.
The sow is still outside with her large weatherproof ark and as much straw as she wants; some very wet days she seems to spend most of the day a-bed but most days she's out rootling a lot of the time and is fine as long as I give her some dry straw when she's dragging wet feet and bod in and out of the ark all day.
So now I have decided that, if I can, I will have spring litters only, and any overwintering pigs will have the option of an indoor pen if needed and be let out for exercise and rootling when conditions and their own preferences allow.