Indoors: resilient plant for window sill?

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Find Sansevieria quite tolerant on our south facing window, though the window is shut at night or below freezing weather.

Our Cactii seem to do ok as well, though mainly small in size.

 

I'd avoid plants with thin leaves, a radiator right beneath would spell brown edges and tips.

Something a bit more succulent would be better, such as the Sansevieria already mentioned.

Crassulas are worth looking into, the most common is Money Tree (Ovata) which may flower, but there are a few interesting shapes.

Ikea often has good, resilient houseplants and sometimes quite unexpected ones at very reasonable prices.