How do I stop my kitten from peeing on my bed?

I just adopted two two month old kittens about a week ago. One of them is very small and spends most of her time sleeping on her own cat bed. Last night she peed in my bed for the first time…I was able to get in the wash before it soaked through to the mattress. I put her on her bed for the rest of the night. Then this morning she came over and did the same thing again…I don’t know what to do. I am living in South Korea in a small studio apartment and there are no doors so I can’t keep her out of my bedroom…the whole apartment is my bedroom! I don’t want to get rid of her but I don’t want her to pee on my bed anymore.