It depends on the day....
Most of the time, though it's my sleep shirt and super comfy Nike yoga pants that I got on sale for about $8! If I'm warm, then the pants come off and it's just the sleep shirt and underwear, but more often than not the yoga pants are on and lately a sweatshirt as well (it's been cold in the house lately!)
Even when I'm out and about, errandizing, I change into the comfy clothes as soon as I get home!