Since you want to do the shirt sleeveless, just look for shirt patterns that either button closed down the front or back (I personally think something more along the lines of a 1940s or 1950s style blouse would work) that has a Peter Pan collar (it might have another name, but that's what I've heard it called all my life). You can get one with or without sleeves. If the pattern doesn't have a sleeveless option, you will just have to make a facing to go in the armhole. That's not too terribly hard, but since you are new to sewing, just try to find one that's sleeveless to save you the trouble.
If you get a pattern that closes down the back, you could even attach the skirt to it and make it a full dress. But if not, you can just wear it as two separate pieces. Since the artwork is so basic, you sometimes have to create your own closures and seamlines.