After some Internet research, I determined that the best way to DIY-repair the holes and cracks in the bedroom's plaster walls would be to use Setting-Type Joint Compound. This comes in powder form in a big bag, and you mix it up with water yourself. This is better for plaster repair because it is denser than the pre-mixed joint compound that comes in a tub, so it won't shrink as much as it dries.
Of course, the proportions for mixing listed on the bag were for the whole 18 lbs. Since I'm not repairing the whole neighborhood, I had to play around and figure out my own proportions for a small batch. I used an old laundry detergent scoop for the powder and a small plastic glass for the water.
I discovered that I could mix different consistencies that were better for different purposes: a thicker mix for the initial hole patching, and a thinner mix to make a smoother second coat once the first was dry.