Girls, hi. I want to buy my eldest daughter a bed so she can sleep sep…

Girls, hi. I want to buy my eldest daughter a bed so she can sleep separately. I think I found one with railings that's suitable, but now I'm stuck in my head, I also have a second daughter, and in about 1.5-2 years she will need such a bed too. Maybe it's better to buy a two-tiered one right away? So I don't waste money twice. Our apartment is not big, two separate beds will take up a lot of space. What would you buy?