Before I moved to a warmer climate, I had this problem. Once my feet got cold, I couldn’t seem to warm them myself... socks, slippers, boots just seemed to insulate their coldness. I managed it by trying not to let them get cold in the first place. As soon as I got out of bed or the shower I immediately fully dressed with socks and slippers/boots. If my feet got cold from being out in the snow too long, then when I got back inside I had to take off my shoes and rest my feet on a hot water bottle or heating pad to warm them, then they could go back to being slippered.
For indoors, knee high knit slippers are good, since they’re like a slipper and a leg warmer in one and there’s no gap at the ankle to let in a draft. For outdoors, duckboots are really warm, better than old school moon boots, which seem like they’d be warm but don’t have any insulation in the sole.