I kept a huge old plant in the coldish greenhouse last winter, and wouldn't recommend that....it just barely squeaked a bit of new growth in the spring (which has now replenished the plant, ready for another challenging winter). The true papyrus (not various carex that look similar but are actually hardy) is very frost sensitive...really needs a conservatory or warm greenhouse overwinter. Only other possibility will be the brightest window in your house, preferably cool and humid which is always unlikely in a normal North American home. The other possibility would be a grow light indoors, allowing the higher temps to promote some growth rather than weak and spider mite infested growth by a natual lit window. Overall, these are tough to get thru the winter, most folks just buy new ones same as bedding plants each spring...
Once it’s trimmed down and repotted I bring it indoors into my home office where it sits in a corner with a dim light. It likes it there but I do have to change water in the saucer every now then to remove surface slime of algae or critters.
