Azhure,
I have houseplants year-round, and it gets to 30 below here sometimes. I keep my plants near lamps(regular table lamps), using compact fluorescent(spiral)bulbs. They don't necessarily thrive, but they do ok through the winter. You want to hold back on fertilizing during the winter as this is a dormant time for most plants, starting them back on a feeding schedule in the spring. Some do well all year inside, like African Violets, Spider Plant, and a few I will put out in nicer weather, but not full sun for the summer...Tradescantia(Wandering Jew), Swedish Ivy, Philodendron. I also have over wintered hot pepper plants this way. Hope this helps.

"I also realise that cyclamens like the cold, and I have it close to a door so it can get a whiff of cold air when it opens. Is that ok?"

Probably not. That air's a little TOO cold, and irregular frigid drafts are hard on plants.

You might want to invest in a cheap humidifier. That will help things a LOT, getting the humidity up.

FYI:

Cyclamens sometimes go dormant during winter, their leaves yellow & then drop & the plant looks awful. I've had this happen & have seen the same for my sister. I no longer try to grow this (I only grow indoors).

how do you stand a 45-50* house!? the plants would probably take it bettter than me if I was in that situation! How did everything turn out? Did you at least buy a space heater. if not for your plants, but yourself :)

Your plants will be fine, as long as their soil is kept on the 'dry side' if the indoor temperatures are truly @ 45-50°, and not any lower than that.

I have many plants near my windows, and as long as they're at least a few inches away, they never incur any damage, (unless it gets well below zero outdoors.)